The Ostracod Genus Actinocythereis From The Middle Miocene of Northern Iraq

Four species and one subspecies of the trachyleberid Ostracod genus Actinocythereis from the lower Fars Formation (Middle Miocene) of Northern Iraq are described for the first time. All of them are new and they show strong affinities with the species described from the Tertiary of Western India.

Description. Thick-shelled, elongate carapace, subrectangular in lateral view with greatest height at the eye tubercle; greatest length nearly at mid-height. Anterior end rounded, with distinct thick anterior marginal rim, decorated with double row of small nodes, posterior and subtriangular slightlypointedcentrally,decorated with row ofsmallnodes. Dorsal and ventral margins straight and nearly subparallel, anterior and posterior cardinal angles more distinct in the left valve. Surface coarsely ornamented with different sized tubercles. The median row runs obliquely anteroventrally to posterodorsally and consists of five tubercles of which the posterodorsal tubercles are smaller than the two anterior ones; the ventral row which lies below the median row is formed of four to five tubercles, the middle two of which are double; there is acurved dorsal row ofeight tubercles, which anteriorly dips below the prominent eye tubercle, some of the posterior ones are doubled. The rows of tubercles form the elevated parts of the shell with shallow furrows in between.
There is a more distinct furrow behind the anterior marginal rim, which is bounded dorsally by a thick short ridge, which is connected with a small node between the eye tubercle and sub-central tubercle. In dorsal view, posterior end narrower K h al a t than the broadly rounded anterior end, tubercles are prominent and break up the outline of the carapace and the maximum width and thickness is at the middle. Internally deep valves; marginal zone moderately broad, marginal pore canals numerous, simple some clustered. Line of concrescence and inner margin coincide and runs subperipherally and is not strongly developed, strong anterior flange in both valve, muscle scarscannot be seen due to thick shell. Normal pore canals not numerous and of open type. Hinge in the left valve consists of an anterior deep rounded socket separated from the eye sinus by a thick curved ridge, a strong postjacent outstanding antero-median tooth, separated from deep quadriloculate posterior socket, by a thick crenulate elongate bar which terminates with a slight node above the posterior socket. In the right valve, a strong outstanding anterior tooth is followed by a deep postjacent socket, bounded by strong ridge emerging from the anterior tooth, a shallow crenulate posteromedian groove and a strong subconical posterior tooth. Sexual dimorphism marked, the presumed males more elongate and narrower than the presumed females; dimorphism is most distinct in dorsal view. Remarks The present species shows affinities with Ac,tiiior,vtlzc.rc.is ritnwfuc,critis (Lyubimova and Guha, 1960) but the ventral margin of the latter species is strongly concave medially, and the posterior end is more rounded than that of A . Description. Medium-sized carapace, elongate subrecrangular i n lateral view, greatest height through the anterior cardinal angle, greatest length at mid-height. Anteriormargin obliquely rounded, decorated with adouble row ofnodes, the inner one starting below the eye tubercle with small nodes which coincide in some specimens and form a thick anterior marginal rim which becomes thin along the ventral margin and terminates posteriorly with small node. The outer one form.; the marginal flange, with fine marginal denticulations along the anterior margin of some specimens. In the male left valve posterior margin subtriangular, smooth. slightly curved in the upper part, with marked posterior cardinal angle. sloping down decorated with 4-5 small nodes in the lower part, pointed in the middle; in the male right valve the posterior end i s slightly concavc in the upper part, curving down in the lower part. In the female the posterior end is concave in the upper part sloping down in the lower part and K h a I n f decorated with small nodes. Dorsal margin straight, jagged with small nodes and shallow furrows in between, the distinctive one behind the eye tubercle, running diagonally, bounded ventrally by a fine ridge which springs from the eye tubercle to join the subcentral tubercle. Anterior and posterior cardinal angles pronounced, ventral margin straight in male, concave anteriorly, curving upwards posteriorly in the female. Lateral surface decorated with tubercles or nodes which are variable in size. The median row starts anteroventrally, runs obliquely posteroventrally and consists of six nodes of which the anterior two are larger. The ventral row consists offour to five small nodes of which the first anterior two are double, these nodes are bounded ventrally by a short distinctive ridge. The dorsal row consists of seven to eight small nodes with shallow furrows in between, which break up the dorsal margin outline. There is a rounded, prominent eye tubercle and prominent, ovate subcentral tubercle. Left valve larger than the right valve, overlapping it more distinctly along the posterior and ventral margins. Inner lamellar moderately wide with a distinct flange projecting anteriorly; line of concrescence and inner margin coincides and runs subperipherally to the outer margin. The selvage runs parallel to the anterior and posterior margin, not seen at midventral margin. Marginal pore canals are fairly numerous especially in the anterior portion. The muscle scars are typical of the genus, normal pore canals are fairly numerous, small and open. Hinge in the right valve consists o f a strong outstanding anterior tooth, swinging ventrally with a short curved ridge to bound the deep, rounded postjacent socket, the posteromedian element is represented by a shallow, strongly crenulate, elongate groove, followed by a strongly outstanding subovate, posterior tooth with flattened surface. Eye sinus, deep very pronounced, below the anterior tooth. In dorsal view, the carapace outline is broken up by rows of lateral tubercles, anterior end broadly rounded, posterior end narrower and strongly pointed centrally, maximum width and thickness at the middle. The left valve strongly overreaches the right at the posterior cardinal angle. the sexes are easily distinguished, the males being more elongate, narrower and less high than the presumed females. This sexual dimorphism is well pronounced in dorsal view.

Dimensions of figured specimens.
Holotyped carapaceHU.277T.3Spl. 1 , fig.7 Remarks The Burmese subspecies 7'i~uc~hylchc~i.is (Ac,tiizocyther.ei.s) hirwunicu kvuiikkokeiisis Gramann, I Y 75 has some similarities to the present species, but differs in being smaller and characterised by a single large node in the posterodorsal part of both valves, which is absent in the Iraqi species. Gramann's species has a very narrow rounded posterior end, which is substriangular in the present species.
In dorsal view, A. costutu sp. nov. is thicker with a pointed posterior end. This species is easily distinguished from other Ac,tiiioc,?lthri.ri.s species by its distinctive posterior shape and the distribution of the lateral nodes. Distribution. This species was found in the Sheikhan. Dohuk, Bai-Hassan, Sheikh Ibrahim and Kirkuk sections of the L. Fars Formation, Northern Iraq.
Ac.tinoiythe,i.ris c~oi~iiuoc~ulrn sp. nov. Diagnosis. A species ofA~,tiiioc:ytho.ri.s with prominent eye tubercle (horn-shaped) standing out strongly from the surface, a distinct posterior cardinal angle and a second dorsal spine sharply pointed backwards, the sexes are easily distinguished with the males more elongate and narrower than the females. of which the outer one consists of fine marginal denticulations; the inner one consists of small nodes in the upper part of the anterior margin and becoming sharp fringe along the lower part. Posterior margin truncated, sloping gently in the upper part, narrowly rounded in the lower. The upper part of the posterior margin is smooth, lower part decorated with a row of sharp spines; dorsal margin straight, sloping gently behind the eye tubercle, obscured in the posterior half by the dorsal spines. Anterior and posterior cardinal angles distinct, the anterior coinciding with the eye tubercle. Ventral margin straight to slightly convex, decorated with small fringes. Lateral surface strongly decorated with rows of prominent nodes and spines, the dorsal one consisting of three spines, sharply pointed upwards (particularly the middle one) and projecting over the dorsal margin; the median row runs obliquely from anteroventrally to posteroventrally and consists of five tubercles, the second of which is the largest and represents the subcentral tubercle; the ventral row consists of three nodes, the first two are small, the third one very large and prominent.  fig.6, L=740pm, H=390pm.

Explanation of
Remarks. The present species has some affinities with Truchy/rheris (Actinocyfhrreis, hirmanica hir-manica subsp. Gramann, 1975, but differs in being higher anteriorly, and wider posteriorly, in having a more distinct posterior cardinal angle and a well developed median row of five tubercles, and in the absence of a large posterodorsal node and in the truncated posterior margin. A . cornuocula sp.nov. is closelyrelated to Actiriocythereis levinsoni Bhatia and Mandwal 1960, but the latter differs in being narrower, in the ventral margin fringed by eight flattened, coalescent spines, in the rounded anterior and posterior ends and the ventral row consisting of four individual tubercles. In addition, the present species differs in its horn-like eye tubercle and prominent, ventrolateral node. Distribution. A . cornuocula was found at the Rashiqa, Dohuk, Sheikhan, Sheikh Ibrahim, and Hamrin localities of Northern Iraq. Description. Carapace elongate subrectangular in side view, greatest height at the anterior cardinal angle, greatest length passing through mid-height. Anterior margin obliquely rounded, decorated with a double row of spines and denticles, the first one consists of about thirty five marginal denticulations, the second one consists of seven small tubercles over the anterior marginal rim. Posterior margin, subtriangular slightly rounded at the middle, smooth in the upper part, decorated with a double row of fine pointed spines in the lower part. Dorsal margin straight, jagged with upward pointing tubercles; anterior and posterior cardinal angles prominent, the anterior one with a distinct eye tu- The ostracod genus 24ctinocytherei.r bercle; ventral margin straight at the middle, converging anteriorly and posterior. Lateral surface marked by three rows of tubercles and spines. The dorsal row consist of five backward-pointing spines which project above the dorsal margin; the median row consists of five, vertically pointing. spines running obliquely from anteroventrally to posteroventrally, of which the largest is the subcentral one; the ventral row consist of three spines, the first two are very small, the ventrolateral one is very prominent with a bifid head. Left valve larger than the right, overlapping conspicuously along the ventral and posterior margins. Inner lamella moderately wide with a distiinct flange; selvage developed peripherally to the outer margin. Hinge in the right valve consists of a strong outstanding anterior tooth, forming a distinct arc ventrally, bounding a deep rounded socket, a flattened, outstanding posterior tooth, separated from the anteromedian element by a shall, longitudinal, crenulate groovt:. There is a marked eye sinus behind the anteroventral margin of thie anterior tooth. Marginal pore canals numerous, some are thickened in the middle. Muscle scars indistinct. Sexual dimorphism marked, the presumed males more elongate and narrower than thle presumed females, and easily disting,uishe<d in dorsal view. In dorsal view both sides are jagged due to the upward-pointing tubercles and spines, anterior end rounded, posteriorly narrowly rounded with the maximum width and thickness behind the middle.
H=390pm. Remarks The present species resembles Actinoc~vthrreis khariensis Khosla and Pant, 1982, but differs in having a broad anterior margin, straighit ventral margin, and in details of ornamentation of which the ventral row has two small nodes ,and a large ventrolateral one instead of the four small nodes of Ac.tinoc~ytherei.s khurimsis. In addition, the posterior margin of the Indian species is narrower than that in the Iraqi species.
Actinotythrreis kutchrnsis has some similarities to the present species, but differs in the shape of the tubercles, which are mostly rounded in shape. with a distinctive tubercle over the posteroventral comer which is not seen in the Iraqi species. Distribution. This species was found in the Bashiqa, Sheikhan, Dohuk, Sheikh Ibrahim and Kirkuk sectionsof the L.Fars Formation of Northern Iraq. Dorsal margin straight, broken by the row of small nodes, ventral margin slightly convex, merging evenly into the anterior margin; joining the posterior margin with a posteroventral spine. Anterior margin obliquely rounded, decorated with a double row of small nodes and denticles. Anterior marginal rim distinct, posterior margin subtriangular to slightly rounded at the middle, decorated with fine spines, more conspicuous ventrally. Lateral surface omamented with spines and nodes which are not well developed, the biggest one being the anteroventral tubercle, the spines more distinct posteriorly. Eye tubercle small and rounded, subcentral tubercle marked. Marginal area moderately broad, line of concrescence and inner margin coincide, selvage well developed running peripherally to the outer margin. Marginal pore canals moderate in number and elongate; some of them are paired in the anterodorsal part. Posterior marginal area narrower with fewer marginal pore canals. Sexual dimorphism pronounced, the presumed males more elongate and narrower than the presumed females.  fig.10, L=8 IOpm, H=460pm. Remarks The present species differs from A . cornuocwla sp.nov. in having a distinctive posteroventral spine developed in the right valve only, and in the tubercles being comparatively weakly developed compared with other Ac.tinocythrr-eis species. The present species shows some similarities to A d noc,ythrJrris spinellosa var. valdiyai Singh and Misra 1968, but the latter differs in being narrower, with well developed tubercles and spines coupled with the absence of a posteroventral spine, which is diagnostic in the present species. Distribution. This species was found at the Bashiqa and Dohuk localities of Northern Iraq.