CUCULLrEA. 



Genus — Cuoull^a, Lamarck, 1801. 



['Syst. Anim. sans Vert.,' j>. 116.] 



1. Lower Cretaceous Species. 



Cucull^ia Porbksi {Pictet and Gampiche), 1866. Plate IX. 



1845. Aeca exaltata (?), E. Forbes (nou Nilsson). Quart. Joura. Geo]. Soc, 



vol. i, p. 245, pi. iii, fig. 5. 

 1850. — gabrielis, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 80 (parfim). 

 1854. Cucull-Ea gabrielis, J. Morris. Cat. Brit. Foss., ed. 2, p. 197. 

 18(56. Arca Forbesi, F. J. Pictet and G. Campiche. Foss. Terr. Cret. de Ste. 

 Croix (Mater. Pal. Suisse, ser. 4), pt. 3, p. 471. 



Description. — Shell stout, much inflated, regularly convex, trapezoidal, in- 

 equilateral. Anterior margin shorter than the posterior, and forming with the 

 hinge-line about a right angle. Ventral margin slightly curved, or in part nearly 

 straight, sloping posteriorly. Posterior margin nearly straight, oblique, forming 

 with the hinge-line an obtuse angle, and with the ventral margin a rounded acute 

 angle, which is usually the most ventral part of the shell. Umbones prominent, 

 incurved, pointed, widely separated, with a sharply defined carina extending to the 

 postero-ventral angle, and cutting off a flattened postero-dorsal area, which is 

 sharply bent with regard to the rest of the valve. Hinge-area very large, with 

 numerous close-set ligament-grooves; margins curved, bounded by a ridge. 

 Ornamentation consists of many slender, sharp, radial ribs, separated by rela- 

 tively broad and shallow grooves, which are crossed at regular intervals by fine 

 concentric ribs. On the anterior part of the shell the radial ribs become more 

 prominent and less numerous. On the postero-dorsal area, except near the umbo, 

 the radial ribs are much less distinct than elsewhere, but numerous radial strias 

 crossed by lines of growth are seen. Hinge-line long, sometimes five-sixths of the 

 length of the shell. Central teeth numerous, perpendicular; lateral teeth few, and 

 parallel to the hinge-margin. 



Measurements : 



(i) 

 Length ..... 86 

 Height 77 



Thickness . . . .80 



(2) 



(^ 



(4) 



(5) 



79 



72 



63 



63 mm, 



76 



60 



65 



58 „ 



95 



71 



70 



72 „ 

 7 



