Recent Bairdiinae (Crustacea, Ostracoda) from the Solomon Islands

The Bairdiinae of the littoral and inner shelf of the Solomon Islands are both abundant and diverse. A total of 21 species have been recovered of which 13 are described as new 2 further species are left in open nomenclature. The new genus Mydionobairdia is erected, based on Triebelina schyroconcha Maddocks, 1969. The new species are: Bairdoppilata paraalcyonicola, B. paracratericola, Neonesidea paragierloffi, N. vscripta, N.? crepidula, N.? rara, Paranesidea bipustulosa, P. corbita, P. equipunctata, P. petalona, P. stricta, P.? confusa and P.? paucipunctata. Some of the difficulties involved in distinguishing species of Neonesidea and Paranesidea are discussed.


INTRODUCTION
Although there has been a considerable number of recent studies on the Ostracoda of the Indo-Pacific, the fauna of the Solomon Islands remains virtually unknown despite the zoogeographical importance of this region stituated as it is between the Polynesian, Indonesian and Australasian regions. The present paper is the first in a series in which this fauna will be described. Harding (1962) described five new nonmarine species recovered from the gut of fish. Apart from this, the only published work is by Whatley & Titterton (1981) who describe two new species and a new genus from marine environments. However, three unpublished theses produced at Aberystwyth reveal more than 170 Miocene to Recent species (Hughes, 1977a MS;Williams, 1980 MS;Titterton, 1984 MS).
This study is based on a series of sediment samples collected using a simple pipe dredge or by diving, by G. W. Hughes in Honiara Bay (samples 13-65) and by C. C. Turner in the same area (Samples 1-5). Their location and approximate depth is given in Fig. 2. An additional six samples (samples OS1-OS6) were collected by Turner from the northwestern coast of Shortland Island (Fig. 3). These samples from Shortland Island and samples 1-5 from Honiara Bay were the only ones to be preserved in buffered formalin.
Type specimens prefixed 1986. Numbers 438 to 500 are deposited in the collections of the Zoology Department, British Museum (Natural History). Specimen numbers prefixed RT/SIR (Rosemary Titterton/Solomon Islands Recent) are deposited in the Mircropalaeontology Museum, Department Geology, University College of Wales, Aberystwyth.

THE BAIRDIINAE
This subfamily are an important and often dominant group in shallow, tropical and sub-tropical seas, particularly in reef and reef-associated environments, where both their diversity and incidence reach high levels. They are particularly well represented in the Solomon Islands and dominate many of the sediment samples.
Recent members of this group were revised by Maddocks (1969), who proposed two new genera, Neonesidea and Purunesidea, which, together with Bairdoppilara Coryell, Sample & Jennings, 1935 and Triebelina Bold, 1946, were used to accommodate many species which had previously been referred to Bairdia McCoy, 1844, which genus Maddocks confined to the Upper Palaeozoic.
In our study of the Bairdiinae of the. Solomon Islands, some difficulty was encountered in accommodating certain species within established genera. For example, some species which seem closest to Noensidea cdar 1 aoE , * % = u  possess characters which are, according to Maddocks, diagnostic of Paranesidea and vice versa. Some species possess characters which have not been previously described in any of these genera. Maddocks (1969) was aware of the shortcomings of her proposed classification in indicating that both Neonesidea and Paranesidea contained different morphological groups probably worthy of subgeneric status. She recognised at least three species with some characters intermediate between Neonesidea and Paranesidea and also remarked on a degree of convergence between species of Paranesidea and Triebelina.
The general validity of Maddocks classification can be demonstrated in that, with respect of Neonesidea and Paranesidea, most species can be readily accommodated within one or other of the two genera. There remains, however, a persistently difficult group of species which seem to possess an amalgam of the diagnostic characters of both genera. A possible solution to this problem is to more clearly distinguish those characters which are of greatest classificatory value, to employ them and to downgrade characters of lesser significance. This, however, tends to lead to reliance on single characters, such as auxiliary dentition to recognise Bairdoppilata. Bolz (1971), in his study of the Late Triassic Bairdiidae and Healdiidae considered this problem and concluded that the "previous taxonomic conception" of the Bairdiidae was too often based on a single morphological character. He concluded that many Triassic genera were invalid and advocated an examination and assessment of "all available morphological features of a species in their interrelations and dependencies from each other. By comparing interrelated groups of markers in different species one may really succeed in establishing units in line with the natural system." In the present study the authors have tried to take into account all available characters in assessing the various taxa encountered with respect to their specific and generic assignments. Certain taxa remain problematical. These are discussed individually below.
Notwithstanding the problems we have encountered, we consider that it is beyond the scope of the intention of this paper and its material, limited as it is by its geographical confines, to attempt a revision of the Bairdiinae at the generic level. genus with auxiliary dentition of 4-6 teeth in R V and dorsal contact groove of RV with distinct locellae. Topotypic material from Maddocks collection from Madagascar, has been examined and compared with the present species. Bairdoppilata alcyonicola is very similar but is smaller and differs in shape, particularly posteriorly being slightly more caudate and the posterior extremity is more dorsal than in the present species. The pattern of the opaque patches (fig. 5, nos. 1-2) is more simple and well defined in the present species, covering a smaller surface area. Insufficient specimens were available to ascertain sexual dimorphism with certainty, but some right valves were much larger than others; they may represent females. B. paraalcyonicola is densely and finely punctate, while B. paracratericola sp. nov. is coarsely punctate (more typical of the genus Paranesidea). Distribution. Samples: 1,2,13,14,15,16,29,0S5,0S6, Guadalcanal and Shortland Islands. sp. nov. (Fig. 5,P1. 1, Derivation of name. L. from the similarity in overall morphology of this species to B. cratericola Maddocks, 1969,  Anterior asymmetrically rounded; anterodorsal slope slightly concave ; anteroventral slope broadly convex; apex almost a right angle at mid-height in LV, just above mid-height in RV. Posterior cavolate, upswept, more so in RV, extremity well below mid-height; posterodorsal slope gently convex, concave near extremity; posteroventral slope more convex in LV than RV. Weak marginal frill antero-and posteroventrally in RV and posteroventrally in LV; small, spinose denticles anteroventrally in LV. Dorsally convex in LV; straight and inclined to posterior in RV. Cardinal angles rounded. Ventral margin gently biconvex, RV with pronounced convexity anteroventrally . Maximum length below mid-height in LV, well below mid-height in RV; maximum height median in LV, at anterior 1/3 of length in RV; maximum width median. Lateral surface covered with large, circular punctae, decreasing in size peripherally, absent around margins, generally concentric about mid-point. Internal features typical of subgenus but R V dorsal contact groove with distinct locellae along ventral half, smooth dorsally.  (Williams, 1980, MS). Samples: 1,2,13,14,15,16,20,29,30,53,54,55,56,57,58,60,OS6,Guadalcanal and Shortland Islands. Genus Neonesidea Maddocks, 1969 Neonesidea schulzi (Hartmann, 1964) sensu Zato (Fig. 5,P1. 2, (Hartmann, 1964  Remarks. This species in its shape, surface ornament, marginal denticulation and internal characters is characteristic of the genus Neonesidea. It may be distinguished initially by its single, elliptical central opaque patch.

Bairdoppilata paracratericola
There is a great variation in size in the adults and A-1 juveniles in the present material; some A-1 instars are larger than the smallest adults; although there is a continual range in size. Details can be seen in Titterton (1984, MS). This variation in size indicates the probable presence of more than one species or subspecies. The lack of soft parts and distinctive size clusters precludes accurate and consistent identification of these very closely related species. All specimens at present are, therefore, placed in N . schulzi. A study being conducted by K. Watson (in press) o n the ostracod faunas from reefal environments in the Java Sea, has allowed this problem to be more satisfactorily resolved, due to the availability of more bairdiid material. Watson (verb. comm., 1987) discriminates two further new species within the N. schulzi plexus sensu this work. Distribution. Miocene, Midway Island (Holden, 1976). Quaternary, Indispensible Reefs, Solomon Islands (Williams, 1980, MS). Recent, shallow water and [14][15][16][17][18][19][20][21][22][5][6]pi. 4, fig. 6.

Recent.
Description. Large to very large. Moderately thinshelled. Translucent with central oval opaque patch and two smaller patches at posterior extremity and anterodorsal angle. Shape typical of genus in lateral and dorsal views. Anterior asymmetrically rounded: anterodorsal slope gently concave ; anteroventral slope broadly convex; apex a pronounced right angle above mid-height. Posterior slightly upswept, acuminate, extremity at mid-height in LV, below in RV, posterodorsal slope straight becoming strongly concave towards extremity; posteroventral slope convex with 12 small, triangular marginal denticles in LV only.
Remarks. This species differs from the N . schulzi in that the posterior is upswept so that the posterodorsal slope is concave. This feature, and the consistent presence of anterior and posterior opaque patches, distinguish it from N . schulzi to which it is most similar among the present material. It most closely resembles N . gierloffi (Hartmann, 1959) from Recent sediments from El Salvador in shape, but differs in that the caudal process is more upturned. Like N . schulzi and N . vscripta in the present material, N . paragierloffi is very variable in size with a difference of over 0.20 mm in length between the largest and smallest adults. Distribution. Samples: 1,2,5,13,14,15,16,17,19,29,30,45,53,55,56,57,58,Guadalcanal. Neonesidea vscripta sp. nov. (Fig. 5,PI. 2, Derivation of name. L. With reference to the v-shaped central opaque patch. Diagnosis. Typical Neonesidea in shape ; dorsal margin asymmetrically convex towards anterior. Valve surface with dense, minute punctae. Translucent with large, v-shaped central opaque patch with two small oval patches at anterodorsal angle and posterior extremity. Holotype. LV 1986.455. Material. 59 specimens: 37 adults and 22 juveniles to Type locality and horizon. Sample 14, 1,400 feet offshore west of Point Cruz, Honiara Bay, Guadalcanal, Solomon Islands. 10 fathoms. Medium coral sand. Description. Large to very large. Moderately thinshelled. Translucent with large v-shaped central opaque patch and two small oval patches at anterodorsal angle and posterior extremity. Shape typical of genus in lateral and .dorsal views. Anterior asymmetrically rounded ; anterodorsal slope almost straight, anteroventral slope convex ; apex above mid-height. Posterior acuminate, extremity well below mid-height ; posterodorsal slope straight, posteroventral slope convex. Dorsally asymmetrically convex towards anterior in LV; straight in RV. Cardinal angles rounded in LV; pronounced in RV. Venttal margin gently convex in LV; biconvex in RV. Maximum length below midheight; maximum height median in LV, at anterior 113 of length in RV; maximum width just anterior of mid-length. Lateral surface densely covered with minute punctae. Internal features typical of genus.   This species possesses a unique v-shaped central opaque patch. Although N . vscripfa, like N . schulzi, has the characteristic shape of the genus, detailed analysis of their outlines show N . vscripfa to be relatively higher dorsally, less tapering posteriorly, lacking a posterior spine in the LV and the dorsal margin is asymmetrically convex so that the posterodorsal slope is less convex towards the posterior extremity. Neonesidea kauaienensis Holden, 1967 from the Neogene to Recent of Hawaii, is similar in shape but is about 0.6mm longer, possesses a different muscle scar pattern and wider vestibulae.

Explanation of Plate 2
The adults show a similar range in size as N . schulzi and N . paragierloffi in the present material. Distribution. Quaternary, Indispensible Reefs and offshore Guadalcanal, Solomon Islands (Williams, 1980, MS) . This species is tentatively assigned to Neonesidea because the finely punctate surface ornament, its muscle scar pattern and smooth hinge are typical of the genus. However, its elongate, subrectangular shape is not typical. In addition, the antero-and posteroventral margins in the LV bear spinose marginal denticles. The present material has been compared with S.E.M. photographs of the type specimens of N. woodwardiana which is very similar in shape but is 0.2mm longer and possesses 4 wedge-shaped scars, whereas the present species has a rosette pattern of 8 wedge-shaped scars encircling a central scar. In addition, N. woodwardiana possesses opaque patches (illustrated by Puri & Hulings, 1976); the present species does not. Distribution. ?Quaternary, off Guadalcanal, Solomon Islands (Williams, 1980, MS)   Remarks. The shape of this species is unusual in that the posterior extremity is ventral and the valves are strongly inflated medianly. Although the species is typical of Neonesidea in many features, particularly its surface ornament, its shape is not; the central muscle scar is also unusual. Neonesidea dinochelatu (Kornicker, 1961) from Recent sediments from Bimini is most similar in shape, in possessing a posterior selvage notch and variable muscle scar, but differs in that the dorsal margin is longer and more inclined posteriorly and the hinge is weaker. The tendency for the dorsal and ventral scars to form single scars and the inflated, smooth carapace indicate a relationship with Aponesidea Maddocks, 1986 (Recent, Bermuda). The present species differs from A . iliffei, the only species described, in that the maximum width of the carapace is median, and not at a quarter of the height; it possesses a central opaque patch and it lacks marginal denticles in the left valve with only very small, marginal denticles posteroventrally in the right valve and not a marginal frill. Until the full scope of the genus Aponesidea can be established, the present species has been questionably assigned to Neonesidea. Distribution. Samples: 1, 13, 14, 15, OS6, Guadalcanal and Shortland Islands.   Maddocks, 1969 recorded in Recent sediments from Nosy Be, Madagascar, is of a similar shape but differs in muscle scar pattern and in possessing a caudal spine. Neonesidea dinochefata (Kornicker, 1961) from the Recent off Bimini, is also of a similar shape but is larger than the present species and the anteroventral slope is less broadly convex. Distribution. Samples: 1,14,15,32,33,54,55,56,58,Guadalcanal. Neonesidea? sp. B (Fig. 6 Hartmann, 1978, from the Recent of Western Australia, is closest, but is less convex dorsally. Adult size measurements cluster into 2 groups, this is believed to reflect sexual dimorphism; the larger group represents the females. As soft parts are not preserved this cannot be proven, however, Maddocks (1969) gave size measurements for both sexes in which the females tended to be the larger. Precocious sexual dimorphism is not apparent.
Paranesidea bipustulosa sp. nov. (Fig. 7 Description. Large. Thick-shelled. Translucent with complex opaque patches: subcentral patch shaped like an amphora without handles, anteriorly and posteriorly large, irregular, trifurcating patches. Shape bairdioid in lateral view ; subelliptical in dorsal. Anterior asymmetrically rounded; anterodorsal slope straight ; anteroventral slope broadly convex with 12 marginal denticles in LV; strong, radially striate frill in RV. Posterior cavolate, slightly upturned, more so in RV; extremity just below mid-height. Posterodorsal slope gently convex to strongly concave near extremity; posteroventral slope convex with 10 digitate marginal denticles in LV and strong, radially striate frill in RV. Dorsal margin strongly convex in LV, straight in RV; cardinal angles rounded in LV, pronounced in RV. Ventral margin gently convex in LV; biconvex in RV. Maximum length just below mid-height ; maximum height median in LV, anterior to mid-length in RV; maximum width median. Lateral surface covered with dense circular punctae which decrease in size peripherally, absent around margins. Pustules variably developed on anterior and posterior lateral surfaces, each with large, simple pore. Normal pore canals large, simple, not within punctae. Internal features characteristic of genus.  Maddocks, 1969, from Madagascar. The posterior extremity in P. spongicola, however, is less upturned and the pattern of the opaque patches differs in that they are all joined. The most conspicuous difference between this species and P. fracticorallicola is that the maximum width of the carapace is median, and not ventral, it is also relatively higher. Distribution. Quaternary, Guadalcanal and Shortland Islands (Williams, 1980, MS). Samples: 1,2,14,15,16,17,19,20,30,32,33,53,55,56,57,58,60,62 0.34 0.20 Remarks. This species is closest to P. stricta sp. nov. but the posterior is more upswept, the punctae are less deeply incised subcentrally, the marginal denticulation is stronger and the valves are less inflated. The upswept cavolate posterior distinguishes it from those species of the genus described by Maddocks (1969)  4. The present species differs in that the anterior and posterior extremities are slightly lower. The posterior extremity of P. onsfowensis Hartmann, 1978, described from the western coast of Australia, is less extended and the surface ornament is finer.
Like l? afgicofa in the present material, the range in size observed, particularly of the adult left valves, may reflect sexual dimorphism. Distribution. Samples: 1,2,13,14,15,17,19,20,29,32,54,57,58,60,Guadalcanal. Paranesidea equipunctata sp. nov. (Fig. 7, PI. 7, Derivation of name. L. With reference to the regular nature of the punctae which comprise the ornament of this species. Diagnosis. Shape of LV elongate, suboval in lateral view; RV typically bairdioid. Dorsal margin broadly convex in LV; posterior bluntly caudate in LV; cavolate and gently upturned in RV. Posterodorsal slope more strongly concave near posterior extremity in RV than in LV. Valve surface with deep, dense punctae, of equal size. Narrow marginal frill on anteroand posteroventral margins, opaque patches absent. Holotype. LV 1986.478. Material. 16 specimens: all adults. Type locality and horizon. Sample OS6. Exact location unknown but thought to be from the intertidal zone, near a coral reef, off the north-east coast of Shortland Island, Solomon Islands, in the vicinity of Rokuai Island. Coarse coral sand. Recent. Description. Large. Very thick-shelled. Feebly translucent without opaque patches. Shape of LV elongate, suboval in lateral view; RV typically bairdioid; elliptical in dorsal view. Anterior asymmetrically rounded; anterodorsal slope almost straight to gently concave near extremity ; anteroventral slope broadly convex with narrow, strong marginal frill in both valves; apex an obtuse angle well above mid-height. Posterior bluntly caudate in LV; cavolate, slightly upturned in RV; extremity just below mid-height. Posterodorsal slope convex becoming concave near extremity in LV, straight to becoming concave near extremity in RV. Posteroventral slope concave with narrow marginal frill in RV. Dorsal margin broadly convex in LV; straight in RV; cardinal angles more pronounced in RV. Ventral margin almost straight in LV; biconvex in RV. Maximum length at about mid-height ; maximum height median in LV, at anterior 1/3 of length in RV. This species most closely resembles P. spongicofa in the present material, but the posterior extremity is more dorsal, the dorsal margin is longer and the anterodorsal slope correspondingly shorter. The marginal frill in the RV is less well developed and the present species is approximately 0.15mm longer. In addition, P. spongicofa differs in that the valves are thickened around the anterior and posterior margins. Distribution. Sample: OS6, Shortland Island.
Paranesidea petafona sp. nov. (Fig. 7, PI. 5 , Derivation of name. Gr. With reference to the petallike shape of the central muscle scars. Diagnosis. Typically bairdioid in shape. Valve surface densely punctate, punctae becoming smaller peripherally but denser. 8-10 strong marginal spines anteroand posteroventrally in LV; marginal frill with denticles antero-and posteroventrally in RV. CMS pattern an ovate patch of highly sutured and marginally lobate scars, the bairdioid pattern recognisable. Holotype. LV 1986.483. Material. 49 specimens: 11 adults, 38 juveniles to A-3. Type locality and horizon. Sample 13, 1,800 feet offshore west of Point Cruz, Honiara Bay, Guadalcanal. 11 fathoms. Medium coral sand. Recent. Description. Large. Thick-shelled. Translucent. Typically bairdioid in shape in lateral view; subelliptical in dorsal view. Anterior asymmetrically rounded; anterodorsal slope gently concave, anteroventral slope gently convex becoming concave ventrally with 8 strong spinose denticles in LV; 12 smaller denticles extending from marginal frill in RV; apex a rounded right angle well above mid-height. Posterior acuminate; extremity just below mid-height, more sharply rounded in RV.
Posterodorsal slope straight to concave near extremity; posteroventral slope gently convex with 7 spinose denticles in LV and marginal frill with ragged denticles in RV. Dorsal margin convex in LV, straight in RV; cardinal angles rounded in LV, pronounced in RV. Ventral margin gently biconvex. Maximum length just below mid-height; maximum height median in LV, at anterior 1/3 of length in RV; maximum width median. Valve surface densely punctate ; punctae decrease in size peripherally but are denser. Internal features characteristic of genus, except for central muscle scar pattern which comprises a large oval patch of highly sutured and marginally lobate scars. The unusual, complex central muscle scar pattern of highly sutured scars is very distinctive. A similar pattern was observed in Neonesidea. sp. B in the present material but the present species differs in being more strongly ornamented, less acuminate posteriorly and more inflated ventrolaterally. Nesidea mulferi Fyan, 1916 from the Timor Pliocene, is about 0.5mm longer and the LV is less high than the present species.
The adult valves of this species are all of similar size. Distribution. Samples: 1,2,13,14,15,16,17,30. 41,54,57,58,Guadalcanal. Puranesidea stricta sp. nov. (Fig. 7, Nos. 9-10; PI. 7, Figs. 14-17) Derivation of name. Gr. With reference to the surface ornament, which appears to be punctured all over. Diagnosis. Typically bairdioid in shape ; valves strongly inflated ventrolaterally, robust. Posterior excavated, extremity well below mid-height ; anterodorsal slope gently concave. Valve surface with deep, dense punctae. Opaque. Marginal denticulation weakly developed. Selvage peripheral, forms small "notch" at posterior extremity in RV. Holotype. LV 1986.488. Material. 22 specimens: 12 adults, 10 juveniles to A-2. Type locality and horizon. Sample OS6. Exact location unknown but thought to be from the intertidal zone, near a coral reef, off the north-east coast of Shortland Island, Solomon Islands, in the vicinity of Rokuai Island. Coarse coral sand. Recent. Description. Large. Very thick-shelled. Opaque. Shape typically bairdioid in lateral view ; subelliptical in dorsal view, strongly inflated ventrolaterally. Anterior asymmetrically rounded ; anterodorsal slope gently concave ; anteroventral slope broadly convex with weak marginal denticles; apex a rounded right angle well above mid-height. Posterior cavolate, extremity well below mid-height ; posterodorsal slope straight becoming concave near extremity, concavity more pronounced in RV; posteroventral slope convex with narrow, delicate marginal frill near extremity in RV only. Dorsal margin convex in LV; straight in RV; cardinal angles rounded in LV; pronounced in RV. Ventral margin biconvex; obscured by lateral inflation in LV. Maximum length at mid-height; maximum height median in LV, at anterior 1/3 of length in RV; maximum width median. Lateral surface covered by very deep, dense punctae which are slightly larger and less densely distributed subcentrally ; concentrically arranged around mid-point. Remarks. This species most closely resembles P. peralona sp. nov. but is more deeply punctate, less caudate posteriorly, the dorsal margin is less broad and the muscle scars are not sutured. Distribution. Sample OS6, Shortland Island.

sample length height
Paranesidea? confusa sp. nov. (Fig. 6, Nos. 3-4; P1. 5, Figs. 1-9) Derivation of name. L. With reference to the uncertain taxonomic status of this species. Diagnosis. Shape of LV subtriangular in lateral view; RV subquadrate: subelliptical in dorsal view. LV dorsal margin angularly convex. Posterior bluntly caudate; extremity acutely rounded in LV. Complex pattern of opaque patches with large, suboval central patch and surrounded by smaller variable, irregular patches. Narrow, delicate marginal frill antero-and posteroventrally in RV. Valve surface with dense, minute punctae. Selvage peripheral, forming a small "notch" at posterior extremity in RV. Holotype. LV 1986.496. Material. 81 specimens: 20 adults, 41 juveniles to A-3. Type locality and horizon. Sample OS3, Katufe Island, off the north-east coast of Shortland Island. Medium coral sand from coral reef. Recent. Description. Large to very large. Moderately thickshelled. Translucent with a complex pattern of opque patches: large central patch irregular, suboval surrounded by many variable, irregular patches. Shape of LV subtriangular in lateral view; RV subquadrate: subelliptical in dorsal view. Anterior asymmetrically rounded: anterodorsal slope slightly convex in LV, almost straight in RV ; anteroventral slope convex ; apex rounded; obtuse, just above mid-height: RV with narrow, delicate marginal frill anteroventrally. Posterior bluntly caudate, extremity well below mid-height, more acutely rounded in LV. Posterodorsal slope convex to gently concave towards extremity ; posteroventral slope convex. LV with 10-12 small, triangular marginal denticles, RV with narrow, delicate marginal frill posteroventrally . Dorsal margin angularly convex in LV; straight, obliquely sloping to posterior in RV; cardinal angles rounded. Ventral margin almost straight in LV; biconvex in RV. Maximum length well below mid-height; maximum height median in LV, at anterior 1/3 of length in RV; greatest width at anterior 1/3 of length. Valve surface with dense, minute punctae. Internal features, in particular the central muscle scar pattern characteristic of Paranesidea.  Remarks. The muscle scar pattern and marginal denticulation of this species is typical of Paranesidea but the surface ornament of very fine punctae and shape of the LV are more typical of Neonesidea. Neonesidea parilihamata Maddocks, 1969 recorded from Madagascar is similar in shape but the dorsal margin is less angularly convex and the muscle scar pattern differs. The adults vary greatly in size, although the A-1 instars are all of a similar size. Distribution. Samples: 13,15,17,30,58,OS3,OS4,OS5,OS6,Guadalcanal and Shortland Islands. Paranesidea? paucipunctata sp. nov. (Fig. 7,PI. 8, Derivation of name. L. Referring to the sparsely punctate surface of the adult. Diagnosis. LV suboval in lateral view, RV typically bairdoid ; strongly inflated dorsally. Very robust. Translucent with large subcentral opaque patch ; skittle-shaped in LV; larger, capstan-shaped in RV. Valve surface with fine, sparse punctae in adults and A-1 juveniles; stronger punctae in younger juveniles. Caud-al spine and small marginal spine antero-and posteroventrally in LV. Holotype. LV 1986.491. Material. 133 valves: 29 adults, 104 juveniles to A-4. Type locality and horizon. Sample 17. Description. Large to very large. Very thick-shelled. Translucent with large subcentral opaque patch, skittle shaped in LV, larger, capstan-shaped extending to dorsal and ventral margins in RV. LV suboval in shape in lateral view, RV typically bairdioid. Anterior asymmetrically rounded ; anterodorsal slope almost straight, gently convex in LV, concave in RV; anteroventral slope broadly convex with 16 small spinose denticles in LV; apex well above mid-height. Posterior bluntly caudate in LV; slightly more cavolate in RV; extremity well below mid-height ; posterodorsal slope gently convex in posteroventral slope convex with approximately 15, small spinose denticles. Stong posterior caudal spine in LV. Dorsal margin strongly convex in LV; straight in RV; cardinal angles rounded in LV, pronounced in RV. Ventral margin biconvex ; obscured by lateral inflation particularly in LV. Maximum length well below mid-height ; maximum height median in LV, at anterior 1/3 of length in RV; maximum width median. Valve surface with very fine and sparse punctae in adult and A-1 juvenile; strong punctae in younger juveniles.  The shape of the LV and the fine ornament of the adults and A-1 juveniles of this species are not typical of Paranesidea although the A-2 and younger juveniles are more typical of the genus. The central muscle scars pattern of this species, however, is typical of Paranesidea. The present species conforms fairly closely with Brady's (1880) original description and illustrations of Bairdia globulus but differs principally in the pattern of the opaque patches and in shape. Hartmann (1978) illustrated a RV of an unnamed species of Bairdia from the northwest coast of Australia, which is similar, but is more strongly caudate posteriorly and more strongly punctate.
The large range in size of the adults and A-1 juveniles may reflect sexual and precocious sexual dimorphism, although the sizes do not fall into distinct clusters. Distribution. Samples: 1,2,13,14,15,16,17,19,29,30,32,45,56,57,  Onotoa, Gilbert Islands and the Flores Sea by the fact that in the type species the dorsal surface of the alae are covered with coarse pustules which are absent in the present species. In the latter, the alae are somewhat more recurved, and the nature of the anterodorsal and posteroventral marginal denticles in the two species is also distinct, those of the type species being more regular and less strongly developed. Distribution. Sample OS6, Shortland Island. The type material is from the Ontong Java Lagoon.

6-12. length height
Ocean (Keeler, 1981, MS Maddocks, 1969. Derivation of name. Gr. Mydion a boat. From the overall resemblance of this genus to a boat. Diagnosis. A small robust genus of the Bairdiinae, subrhomboidal in lateral view, subcylindrical to subelliptical in dorsal view. Anterior margin with long convex antero-ventral slope and apex above mid height; posterior margin with subventral apex and long straight or slightly concave posterodorsal slope. Dorsal surface covered with small spines and papillae. Long thin marginal spines anteriorly and posteroventrally. Hinge adont, narrow. Auxiliary dentition absent. Adductor muscle scars usually 8 in two obliquely curved rows. Remarks. This genus is closely related to Triebelina but differs in its more elongate and subrhomboidal shape and in lacking the ribs and strong punctate or reticulate ornament of that genus. From Papillatabairdia Bentley (1981) it differs in shape (this genus being reniform with a rounded anterior and subrounded posterior margins) and in ornament, Papillafabairdia being densely covered with very small hemispherical papillae. Keij (1974, p. 346) doubted that Triebelina schyroconcha belonged to Triebelina because of its unusual shape and ornament.
There are other species in the subfamily which somewhat resemble M. schyroconcha in shape, such as Bairdia hanaumaensis Holden, 1967, from the late Cainozoic and Recent of Hawaii, but this species is densely and minutely punctate. Bairdia sp., Allison & Holden, 1971, while similar in shape, is punctate. These two species and a number of as yet undescribed species known to one of us (RCW) from Indonesia could be subsequently included in Mydionobairdia if the diagnosis was amended to embrace punctate species.

Mydionobairdia schyroconcha
and not punctate. Maddocks, 1969 (Recent, Madagascar) is considered by her to be questionably synonymous with B. tuberculata Brady of Brady, 1880 and 1890, but not with B. tuberculata Brady, 1867 (= B. rhomboidea Brady (non Kirkby)). The species illustrated by Maddocks is almost certainly conspecific with the present material and material from the Java Sea (Karen Watson pers. comm., 1986). Hartmann (1978Hartmann ( , 1981 illustrates a species h e assigned to Bythocypris from the Recent of Australia, which resembles the present species in possessing a spinose ornament, but it is less acuminate posteriorly. This species should be included in Mydionobairdia.

Triebelina schyroconcha
In the present study M. schyroconcha was recovered from samples 1, 14, 58 in Honiara Bay, Guadalcanal and sample OS6, Shortland Island. length height