94 DIMY ARIA. PACHYMYA. 
one is elevated into a sharp-edged plate or ledge projecting 
from the side of the shell; margin angulated, or with an 
eared, produced border, hinge rectilinear, or with a series 
of angular, somewhat irregular teeth, set transversely, very 
small near the umbones, longer and more obiique towards 
both extremities : covered by an epidermis. 
Cucullea glabra. Plate VIII. fig. 12. 
A small portion of the anterior side of the area remains uncovered by the 
ligament ; the area increases in size by age, and is transversely grooved in the 
adult state : an obtuse angle renders the anterior portions of the shells distinct, 
and when the valves are shut, and that side alone presented to view, it is cor- 
diform, and longitudinally produced in the centre. The larger valve is more 
intensely coloured, with stronger markings inside ; the smaller one being paler 
in colour, with more distinct and closer set striz than the opposite valve. 
Only one recent species of Cuculleze is known, it inhabits the Ocean. 
Several fossil species have been found in the Greensand ard in the inferior 
Oolite of Britain, and at Grignon, Bordeaux, and Beauvais, France. 
Genus X1.— AXINUS. — Sowerby. 
Generic Character. —- Shell equivalve, transverse, free, 
posterior side very short, rounded ; hinge provided with a 
Jong, oblique ligament, situate in a furrow, stretching along 
the whole edge; anterior side considerably produced, an- 
gulated, and somewhat obliquely truncated, with a flattish 
lunette near the beaks. 
Axinus obscurus. Plate IX. fig 9. 
Known only in a fossil state. 
Found in the Magnesian Marl, at Colyhurst, near Manchester, and at 
Garforth Cliff, near Leeds. 
TRIBE III.— CARDIACEA, 
Primary teeth irregular both in form and situation, and 
in general accompanied by one or two lateral teeth. 
Genus XII. — PACH YMYA. — Sowerby. 
Generic Character. — Shell very thick, equivalve, trans- 
versely elongated ; sublobate, with the umbones situate 
near the anterior extremity ; ligament short, partly internal, 
and attached to a prominent process, or fulcrum; close at 
both extremities. 
Pachymya gigas. Plate VII. figs. 12, 18 
This singular bivalve has considerably the aspect of a Modiola, but differs 
from that genus in the ligament being attached to a prominent fulcrum: the 
position of the umbones, the elongate shape, and partial separation of the 
anterior portion into a sublobate form, all connect it with Modiola but the 
