CALLISTA. 193 



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

 1866. — — F. J. Pictef and G. Cawjnche. Foss. Terr. Cn't. Ste. Croix 



(Matur. Pal. Suisse, ser. 

 4), p. 190. 

 18G7. — — E. Gueraiujcr. Album Pak'ont. de la Sartho, p. IS, pi. xvii, 



fig. 11. 

 1868. — — A. Briiirt aniJ F. L. Cornet. Meuli'de Bracquegnies (Mem. 



cour. et Mem. des Sav. 

 (■trangers, vol. xxxiv), p. 72, 

 pi. viii, figs. 3 — 5. 



? Nou 1846. Venus plana, A. E. Revss. Die Ver.stein. der bdhm. Kreideformat., pt. 2, 



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



? — 1879. Cytheeea (Cabtatis) 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. Lunula long, cordiform, distinctly limited. 

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

 stronger growth-ridges at intervals. Fine radial ril)bing is occasionally seen in 

 tlie 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, slightl}' diverging, and separated dorsall}^ 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 unil^o ; in front of the 

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

 margins. In tlie li>ft valve the stout anterior and median cardinals diverge from 

 mider tlie uinl)o, tlie anterior tooth l)eing nearly vertical; there is a long slender, 

 obli(|ue posterior cardinal, and an elongate, ridge-like anterior lateral tooth, wliich 

 is grooved or corrugated. 



Measiirr})ii')ifs .- 



(I) (2) (H) (4) (-.) (C) (7) (8) (9) 



Lengtli . 72 (i'.» CO Crl M r,2 1-8 4I. 35 mm. 

 Hciglit . r,3 .-,7 53 51 4.() 43 M 37 29 „ 



(1—9) Blackd.nvii. 



Al}i)iitirs. — Specimens from Senonian deposits of Kurope have been referred to 



