60 
S P O N D Y L U S. 
(Plate VII. Fig. 6.) 
Shell inequivalve, rough. Hinge having two 
recurved teeth with an intermediate hollow ; some- 
times eared. (Fig. 5.) One of the valves convex 
and thick, the other flatter. 
The intermediate sinus contains a connecting 
cartilage, as in some other genera. The lower of the 
two valves of this singular shell is, in many indi- 
viduals of the first species, GcEdaropus, produced 
towards the apex into a projecting beak, one side of 
which is excavated so as to leave a flat space per- 
pendicular to the hinge. Through this the cartilage 
is continued in a curvilinear direction to the very tip. 
The appearance is that of an imperfect specimen, 
having one of the apices artificially mutilated. 
The surface is always coarse and rough, tuber- 
culated or spinous, and more or less pectinated. 
With the exception of the strong and well-defined 
teeth which are peculiar to this genus, and which 
are totally wanting in that of Ostrea, the affinity 
