CUCULLAMA. 49 
Genus—CucutLma, Lamarck, 1801. 
[‘Syst. Anim. sans Vert.,’ p. 116.] 
1. Lower Cretaceous Species. 
Cucutuma Forpesi (Pictet and Campiche), 1866. Plate IX. 
1845. Arca ExaLrara (?), #. Forbes (non Nilsson). Quart. Journ. Geol. Soc., 
vol. i, p. 245, pl. ii, fig. 5. 
1850. — _ Gasrirtis, 4. d'Orbigny. Prodr. de Pal., vol. ii, p. 80 (partim). 
1854. CucuLn®a easrietis, J. Morris. Cat. Brit. Foss., ed. 2, p. 197. 
1866. Anca Forest, F. J. Pictet and G. Campiche. Foss. Terr. Crét. de Ste. 
Croix (Matér. 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 distinet than elsewhere, but numerous radial striae 
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 : 
(1) (2) (3) (4) (5) 
Length . . : : . 8&6 79 72 65 63 mm. 
Height . : ; : A Lt 76 60 65 5G a 
Thickness. : : sO 95 fil 70 COL sy 
( 
