CALLISTA. 193 



1850. Venus plana, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 159. 



1865. F. J. Pictet and G. Campiche. Foss. Terr. Civt. Ste. Croix 



(Mater. Pal. Suisse, ser. 



4), p. 190. 



1867. — E. Gue'ranger. Album Palt'ont. de la Sarthe, p. 13, pi. xvii, 



%• 11. 



1868. A. Briart and F. L. Cornet. Meulede Bracquegnies (Mem. 



cour. et Mem. des Sav. 

 (•trangers, vol. xxxiv), p. 72, 

 pi. viii, figs. 3 — 5. 



? Non 1846. Venus plana, A. E. Reuss. Die Verstein. der bohm. Kreideformat., pt. 2, 



p. 21, pi. xli, fig. 14. 



? — 1879. Cytherea (Caryatis) plana, /. F. Whiteaves. Mesoz. Foss., vol. i (Geol. 



Surv. Canada), p. 149, 

 pi. xvii, fig. 14. 



Description. — Shell oval, sometimes more or less triangular, rounded, moderately 

 convex, considerably inequilateral; length greater than height. Antero-dorsal 

 margin long, concave. Anterior part of valve more or less produced, with 

 rounded margin. Ventral margin forming a considerable curve. Posterior margin 

 short, rounded or slightly truncate. Postero-dorsal margin convex, much longer 

 than the antero-dorsal margin. Umbones rather prominent, pointed, close 

 together, curved anteriorly. Lunule long, cordiform, distinctly limited. 

 Escutcheon not defined. Ornamentation consists of small concentric ridges, with 

 stronger growth-ridges at intervals. Fine radial ribbing is occasionally seen in 

 the posterior part of well-preserved specimens. Pallial sinus fairly large, angular 

 or sub-angular, slightly ascending. 



Hinge : In the right valve the anterior and median cardinals are nearly 

 vertical, slightly diverging, and separated dorsally, the posterior cardinal is 

 oblique, long and divided, its posterior part is much longer than the anterior part, 

 and the latter nearly meets the anterior cardinal under the umbo ; in front of the 

 cardinal teeth there is a shallow, elongate pit with slightly raised upper and lower 

 margins. In the left valve the stout anterior and median cardinals diverge from 

 under the umbo, the anterior tooth being nearly vertical ; there is a long slender, 

 oblique posterior cardinal, and an elongate, ridge-like anterior lateral tooth, which 

 is grooved or corrugated. 



Measurements : 























(i) 



(2) 



(3) 



(4) 



(5) 



(6) 



(7) 



(8) 



(9) 



Length 



72 



69 



63 



62 



54 



52 



48 



44 



35 mm. 



Height 



63 



57 



53 



51 



46 



43 



41 



37 



29 „ 



(1—9) Blackdown. 

 Affinities. — Specimens from Senonian deposits of Europe have been referred to 



