l)()SIN10l'SJ8. iyl 



(Innis — DdsiNlor.sis, T. .1. ('(iiiniJ, IHlJI. 

 (' I'roc. Acad. Nat. Sci. Pliila-ai-lpliia,' |). -JllJ.) 



DoSINIOl'SIS SUliEOTUNl>.\ {Soirrrhlj), 1 830. I'latu XXVIII, lig.S. 1 — (J. 



1836. Cythkb«a subkotunda, ,/. de C. Sowerby. Trans. Geol. Soc, ser. 2, vol. iv, 



pp. 240, :3-il, pi. xvii, tig. 2. 

 1850. Venus — A. cVOrhUjnij. Prodr. de Pal., vu\. ii, p. 159. 



1854. Cythkkea — J. Morris. Cat. Biit. Foss., ed. 2, p. 201. 



1870. Venu.s — /*'. Sluliczka. Paleeout. ludica, Cret. Fauua S. 



India, vol. iii, p. 161 (Caryalis). 



Description. — Shell rather thick, rounded, oval or somewhat orbicular, of small 

 or moderate convexity ; length rather greater than height ; moderately, sometimes 

 considerably, inequilateral. Antero-dorsal margin long, concave. Anterior 

 margin rounded, passing gradually into the considerably curved ventral margin. 

 Postero-dorsal margin very long, convex, witli a considerable ventral slope. 

 Posterior margin rounded. Umbones small, pointed, close together, slightly 

 curved anteriorly. Lunule elongate, depressed, distinctly limited. Escutcheon 

 narrow, depressed, with a sharp border. Pallial sinus rather large, sub-angular. 

 Ornamentation consists of fine concentric striae, and growth-lines. 



Hinge : In the right valve three strong, nearly straight, diverging cardinal 

 teeth, of which the anterior and median are closer together and diverge at a 

 smaller angle than the median and posterior, the last being divided l)y a shallow 

 longitudinal groove; there is a small posterior lateral tooth and an elongate 

 anterior pit. In the left valve the anterior of the three diverging cardinal teeth is 

 nearly vertical, the median is the stoutest, and the posterior is oblicjue and slender ; 

 the anterior lateral tooth is elongate and pai'allel to the lunular margin; the 

 posterior lateral is very small. 

 Measure 1)1 cuts .- 



(1) (2) (y) (t) (5) 



Length . 34 . 31 . 2\) . 28 . 20 mm. 



Height . 32 . 28 . 20-5 . 20 . 2:3-5 „ 



(1 — 5j Blackdowu. 

 Ti/pe. — From Blackdowu; in the Bristol Museum. 

 Distribnilon. — Upper Greensand (zone of Srlduiubuchia ro.slndu) of Blackdown. 



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