CUCULLAA. 61 
CucutLma opesa (Pictet and Roux), 1852. Plate XII, figs. 6, 7a, b, 8a, b. 
1852. Arca opuysa, F. J. Pictet and W. Roux (non Sowerby). Moll. Foss, Gres 
verts de Geneve, p. 464, pl. xxxviii, figs. 1, 2. 
1866. — — FJ. Pictet and G. Campiche. Foss. du Terr. Creét. de Ste. 
Croix (Matér. Pal. Suisse, ser. 4), pt. 3, p. 459. 
1871. — — F. Stoliczka. Paleont. Indica, Cret. Fauna S. India, vol. in, 
p- 343 (TLrigonoarca ?). 
Non 1833. Arca opesa, G. B. Sowerby. Proc. Zool. Soe., pt. 1, p. 21 (figured Reeve, 
Conch. Iconiea, vol. ii, 1848, pl. i, fig. 3). 
Descrviption.—Shell subrhomboidal, rounded, a little inequilateral and oblique, 
much inflated. Posterior border slightly convex, forming an obtuse angle with 
the hinge-line, and joining the ventral border at an acute but rounded angle. 
Umbones prominent, well separated except in young forms. A prominent but 
rounded carina extends from the umbo to the postero-ventral angle. Hinge-area 
long, of moderate breadth, with numerous (often thirteen to eighteen) closely-set 
ligament-grooves. Ornamentation consists of faintly marked radial ribs crossed 
by lines of growth. Hinge with some central transverse teeth, and lateral teeth 
which are parallel or nearly parallel to the hinge-line. Posterior adductor plate 
well marked. 
Measurements : 
(1) (2) (3) (4) (5) 
Length . : ‘ . 98 47 43 28 22 mm. 
Height . : : . 48 42°5 40 25°5 LS) 35 
Thickness ; ; Seri 44, 37 21 iW fameee 
Hinge-line ' : 39 31 26 15 14 ,, 
Affinities. —This is related to C. glabra, Sowerby, but can be distinguished 
from that by its more inflated form, more prominent umbones, more rounded 
outline; the ventral margin is placed more obliquely with regard to the hinge- 
line ; the hinge-line is relatively shorter and the ligament-grooves more numerous ; 
the radial ribs are less distinctly marked. 
Remarks.—The name Arca obesa was pre-occupied by Sowerby for a recent 
species dredged near the coast of West Columbia ; but since the fossil form is now 
referred to the genus Cucullea the specific name may be retained. 
Types.—The types are from the Gault of the Perte du Rhone. 
Distribution.—Gault of Folkestone (zones viii, ix); and Aylesford. Cambridge 
Greensand (derived). Chloritic Marl of the Isle of Wight and Warminster. 
Upper Greensand of Devizes. 
