60 



SPONDYLUS. 



(Plate VII. fig. 6.) 



Shell inequivalve, rough. Hinge having two re- 

 curved 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 sliell is, in many indi- 

 viduals of the first species, Gcedarcpus, 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, tubcrcu- 

 lated or s])inous, 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 Ostrca, the aflinity 



