192 CRETACEOUS LAMELLIBRANOHIA. 



passing- gradually into the considerably curved ventral margin. Postero-dorsal 

 margin long, convex. Posterior margin short, rounded. Umbones prominent, 

 pointed, with a considerable anterior curvature. Lunule ovate, faintly limited. 



Ornamentation consists of growth-rings and (in well-preserved specimens) of 

 numerous small, regular, concentric ribs. Pallial sinus deep, ascending, with 

 rounded end. 



Hinge : In the right valve the anterior and median cardinals are strong, and 

 diverge below the umbo ; the posterior cardinal is long, oblique, curved, and 

 divided into two parts of which the anterior is shorter than the posterior. In 

 the left valve the anterior and median cardinals are strong and diverge below 

 the umbo ; the posterior cardinal is laminar and very oblique. 



Measurements : 



(1) (2) (3) (4) (5) ((5) 



Length . 44 . 40 . 37 . 34 . 32 . 30 mm. 

 Height . 33 . 31 . 32 . 26 . 27 . 23 „ 



(1 — 6) Blackdowu. 



Affinities. — The form from the Aachen Greensand which was referred to this 

 species by Goldfuss and others possesses an anterior lateral tooth. 



Remavlcs. — In Sowerby's figure the lunule projects more than in any specimen 

 which I have seen, but in other respects the examples from Blackdown agree with 

 that figure. 



Type. — The type came from Blackdown, but cannot now be found. 



Distribution. — Upper Greensand (zone of Schloenbachia rostrata) of Blackdown. 1 

 Recorded by Jukes-Browne from the Upper Greensand of Devizes. 



Genu? — Callixta, O.A.L. March, 1853. 

 (' Catalog. Conchyl. de Yoldi,' ii, p. 27.) 



Callista plana (Sowerby), 1813. Plate XXX, figs. 1—0. 



1813. Venus planus, J. Sowerby. Min. Conch., vol. i, p. 58, pi. xx, lower figures. 

 1854. Cytherea plana, J. Morris. Cat. Brit. Foss., ed. 2, p. 201. 

 ? 1845. Venus plana, A. d'Orbigny. Pal. Franc. Terr. Cret., vol. iii, p. 447, pi. 



ccclxxxvi, figs. 1 — 3 (? partim). 



1 The type of Venus submersa, Sowerby, from the Upper Greensand of Pinhay, cannot be found. 

 I have seen no specimen which could be referred to that species. Barrois, however, records it from 

 the Upper Greensaud of Lulworth. J. de C. Sowerby, 'Trans. Geol. Soc.,' ser. 2, vol. iv (1836), pp. 242, 

 342, pi. xvii, fig. 4 ; d'Orbigny, ' Prodr. de Pal.,' vol. ii (1850), p. 159 ; Morris, ' Cat. Brit. Foss.,' ed. 2 

 (1854), p. 231 ; Stoliczka, ' Palreont. Indica, Cret. Fauna S. India,' vol. iii (1870), p. 161 (Caryahs) 

 Barrois, ' Terr. Cret. Super, de l'Auglet. et de l'Irelande ' (1876), p. 90. 



