New species of the ostracod genus Neosinocythere Huang (1985) from the Indo-West Pacific Region

Four new species of the ostracod genus Neosinocythere are described from the Indo-West Pacific region: N. indica, N. macropunctata, N. micropunctata and N. indowestpacifica. The diagnoses of Neosinocythere and the subfamily Sinocytherinae Huang are emended.


INTRODUCTION
established Neosinocythere on the single species Sinocythere reticulata Chen, 1982 and placed it, together with two other genera (Sinocythere Hou, 1982 andSpinileberis Hanai, 1961), in the new family Sinocytheridae. Neosinocythere was once thought to be monospecific and endemic to China, where it is found commonly in Miocene to Recent shallow marine and coastal brackish deposits of eastern China (Guan et al., 1978, Hou et al., 1982Gou et al., 1983;Huang, 1985;Zhao, 1985;and others). In the course of our joint study on the Cainozoic Ostracoda of the Indo-West Pacific, we have collected new material of Neosinocythere from Indonesia, Malaysia, the Malacca Straits, India and Reunion, which markedly expands its geographical distribution, showing it to be an important element of the Indowestpacific fauna. The type specimens of the new species and the figured specimens of N . elonpata are deposited in
Emended diagnosis. Small to medium, subrectangular to subtriangular in lateral view with or without caudal process posteroventrally. Surface reticulate, costate, tuberculate or punctate; always with an ocular rib, a prominent subcentral tubercle and its surrounding sulcus. Sexual dimorphism distinct. Hinge modified holamphidont; posterior tooth of RV reniform and slightly denticulate with a shallow ventral concavity, anterior tooth smooth or denticulate; in LV posterior socket always with an anti-slip toothlet ventrally. Inner lamella wide, avestibulate or with very small anterior vestibule, marginal pore canals few in number. Adductor the Department of Zoology, The Natural History Museum, London. muscle scars small in size, consisting of 4 close-packed scars; frontal scar single, oval or heart-shaped. Remarks. Members of the Sinocytherinae are similar to those of the Trachyleberidinae Sylvester-Bradley in hinge and adductor muscle scars but differ in having a prominent subcentral tubercle with a surrounding sulcus, and with posterior anti-slip toothlet of the LV. The posterior anti-slip toothlet of the LV, is similar to "aurilid genera of the Hemicytheridae Puri, but the latter have different frontal and adductor muscle scars. The subfamily bears considerable resemblance to the Orionininae (Hemicytheridae), and Neosinocythere externally is very similar to Caudites Coryell & Fields. These resemblances are superficial; the soft parts and musculature of the two groups are quite distinct. Five genera are included in the subfamily: Cathaycythere Whatley & Zhao, 1986, Neosinocythere Huang, 1985, Sinocythere Hou, 1982 andSpinileberis Hanai, 1961. Distribution. Miocene to Recent, eastern and southern Asia, Indian Ocean, West Pacific.
Genus Neosinocythere Huang, 1985 Type species. Orionina elongafa Hu, 1976 Original description. Valve trapezoid to triangular in lateral view, thick-shelled. Posterior end triangular, surface of valve with two sulci anterodorsally, reticulation, nodes and depression. Hinge of left valve consists of anterior and posterior sockets and middle crenulate bar. Marginal zone moderately broad, with some straight, simple and scattered pore-canals. Vestibule absent. Emended description. Caudal process posteroventrally always present in females, sometimes present in males. Anterior and posterior cardinal angles distinct, and particularly in LV of females where it is swollen to form a prominent hinge-ear. Surface reticulate or punctate; an ocular rib extends from anterior cardinal angle to midanterior, commonly with 3 nodes posteriorly and one node anteroventrally, one thin anterior marginal rim and 4 thin longitudinal (dorsal, median, subventral and ventral) ribs. Median rib extends diagonally from posterodorsal node and is interrupted by the sub-central tubercle. Carapace compressed anteriorly, posteroventrally and posterodorsally. Eye tubercle weakly present. LV overhangs RV dorsally and overlaps it along posterodorsal margin. Hinge modified holamphidont, in RV anterior tooth smooth, tablet-shaped and perpendicular in side view to dorsal margin, posterior tooth short, slightly lobate and curved with a shallow ventral concavity which serves to receive the anti-slip toothlet of the LV; in LV anterior socket always enclosed by a crescentic ventral bar which extends anteriorly from the conical anteromedian tooth, posteromedian bar denticulate. Inner lamella wide, especially anteriorly and posteroventral; avestibulate; marginal pore canals few, widely spaced and mostly simple. Adductor muscle scars a vertical row of 4 small closely adjacent scars; both frontal and mandibular scars are single and ovate. Remarks. Huang (1985) erected Neosinocythere with Sinocythere reficulata Chen, 1982 as type species. S. reticulafa is identified by the present authors as the junior synonym of Atopocyfhere superba Guan, 1978 and Orionina elongafa Hu, 1976. One of the notable features of this genus is the strong sexual dimorphism; the female is not only shorter and higher than the male but also always has a posteroventral caudal process, which is absent in the male of some species, such as N. indica, N. indowestpac$ca and N. macropunctafa. Sinocythere Hou, 1982, the genus most similar to Neosinocythere, lacks the triangular caudal process in both sexes and is the feature on which the two genera are separated. Neosinocyfhere differs from Spinileberis Hanai, 1961 in that the sexual dimorphism in the latter is much weaker and its posteroventral inner lamella is narrow and the posterior nodes are usually not developed.
Neosinocythere elongata (Hu) in deeper shelf down to a depth of some 70m Zhao et al., 1985). Living carapaces have been reported from the estuary of the Yangze River from a salinity less than 25%0 (Zhao, 1985).
Neosinocythere dekrooni (Kingma), 1948 (Pl. 1, figs 8,9) 1948 Cythereis dekrooni Kingma, p.79,80, p1.9, figs 15a,b. 1980 Cythereis dekrooni Kingma, p.200. 1988 Sinocythere dekrooni (Kingma) Fig.3. Paratype F, ALV (1991.347), internal lateral view. Holotype Car. 1991.336 Paratype LV. 1991.337 Paratype Car. 1991.338 Paratype Car. 1991.339 Paratype Car. 1991.340 Paratype Car. 1991.341 Paratype LV. 1991.342 Paratype RV. 1991 (17 females and 9 males). Description. Males subrectancular and females nearly quadrate in lateral view. In males dorsal and ventral margins almost parallel; upper part of posterior margin truncated, lower part narrowly rounded. In females dorsal margin declines posteriorly, and the lower part of the posterior margin protrudes to form a triangular caudal process. Anterior and posterior cardinal angles distinct, particularly in the LV of females. Surface reticulation consists of polygonal fossae and smooth sola, superimposed with 4 thin longitudinal ribs: dorsal rib very feeble, especially in males; median rib not reaching anterior margin; subventral rib ending at posteroventral node posteriorly; ventral rib short and overhung. A thin rib extends along anterior margin, ornamented with very narrow frill. Carapace, especially in females, compressed along anterior, posteroventral, posterodorsal and dorsal margins. The male has weaker posterior nodes and lacks a caudal process. Inner lammela wide anteriorly and posteroventrally, and inner margin markedly protruded inwards in posteroventral area; 7 anterior and 2 posterior marginal pore canals. Remarks. The new species is the largest of the genus. It differs from N. elongata Hu in that the male lacks the posteroventral caudal process, and the sola of the reticulation are smooth. Distribution. Recent of western and eastern coasts of India.

indica.
Remarks. This species is distinguished by its long median rib reaching the anterior margin. The material from the type locality consists entirely of females, the only male carapace recorded (Whatley & Zhao, 1987, p1.2 fig.27) coming from the bottom sediments of the Malacca Straits (Whatley & Zhao, 1987, p1.2 Fig.27