36 CRETACEOUS LAMELLIBRANCHIA. 



1866. Arca aptiensis, F. J. Pictet and G. Campiche. Foss. du Terr. Cret. de 

 Ste. Croix (Mater. Pal. Suisse, ser. 4), pt. 3, pp. 454, 

 471. 

 1871. — — F. Stoliczka. Palseont. Indica, Cret. Fauna S. India, 



vol. iii, p. 343 (Trigonoarca?). 

 ? 1871. — cymodoce, Stoliczka. Ibid., p. 345. 



? 1SS4. — Raulini, O. Weerth. Die Fauna Neocom. Teutoburg. AValde. 



(Palseont. Abhand., vol. ii), p. 47. 



Description. — Shell oblong, a little higher near the posterior part of the hinge- 

 line than elsewhere, very inequilateral. Anterior margin forming a sharp angle 

 (often about 90°) with the hinge-line, and curving evenly to join the ventral 

 margin, which is slightly curved, and has a general slope posteriorly. Posterior 

 margin oblique, slightly convex, forming obtuse and acute angles with the dorsal 

 and ventral margins respectively — the acute angle being somewhat rounded. 

 Umbones not prominent, close together, with a rounded carina extending in a 

 double curve to the postero-ventral angle, and cutting off a concave triangular 

 area. Shell compressed in front of the umbones. Hinge-line about three 

 quarters of the length of the shell. Hinge-area narrow, elongate. Ornamenta- 

 tion consists of well-marked concentric ribs, and numerous fine radial ribs. On 

 the anterior part of the shell, at intervals, some of the radial ribs become more 

 prominent, and curve anteriorly. On the postero-dorsal area, and also near the 

 carina, at intervals, some of the radial ribs are more elevated than the others, and 

 here the concentric ribs are less distinct than elsewhere. Central teeth small and 

 transverse, lateral teeth oblique. 1 



Measurements : 



(1) (2) 



Length 28 . , 37 mm. 



Height 14 . . 21 „ 



Thickness ..... — . 16 „ 



Affinities. — By most authors this species has been referred to Cvcullsea Raulini, 

 Leymerie, 3 to which it is certainly closely related ; in fact, a larger collection of 

 French specimens than I have been able to examine might well show the two forms 

 to be identical. I have not seen the type of B. Raulini, nor the original of 

 d'Orbigny's figures, but other specimens in the d'Orbigny Collection and the 

 Fjcole des Mines, Paris. Stoliczka remarks on the difference between Leymerie's 

 and d'Orbigny's figures of that species, and suggests that either one figure is 

 incorrect or that they represent two distinct species. I think that the two figures 



1 The characters of the teeth are given on the authority of Pictet and Campiche. 



1 ' Mum. Soc. G-eol. de France,' vol. v (1842), pi. x, fig. 1, p. 7 ; d'Orbigny, ' Pal. Franc. Terr. 

 Cret.,' vol. iii (1844), p. 204, pi. cccx, figs. 1, 2; Pictet and Campiche, " Foss. du Terr. Cret. de Ste. 

 Croix " (' Mater. Pal. Suisse,' ser. 4), pt. 3, pp. 440, 469. 



