CONCHOLOGY. 63 



A. antiquata. A. Brasiliana. 



A. rhombea. A. corbicula. 



A. granosa. A. squamosa. 



A. auriculata. A. Cayennensis. 



A. inequivalvis. 



A. Noce. Noah's Ark. PI. 10, fig. 5. 



Species boat-shaped, oblong, striated transversely and 

 ribbed longitudinally ; umbones remote and incurvated ; 

 margins entire and gaping ; hinge straight ; whitish, with di- 

 vergent zigzag chestnut stripes ; inside bluish white. 



A. tortuosa. The twisted Ark. 



A rare species; shell elongated, close, twisted; hinge 

 completely straight. 



A. harhata. The bearded Ark. 



Species with the hinge straight, not hollowed or not gaping 

 inferiorly, and of which the muscle is not adherent. 



3. Pectunculus. Nineteen species. 



This genus has the ligament partially inserted internally, 

 and has no exterior angular groove. The valves never gape, 

 often have rayed longitudinal ribs, are compressed, and the 

 shell by age becomes thick and ponderous, sometimes at- 

 taining a large size. The teeth in the hinge are not so nu- 

 merous as in the Area and Cucullasa; the centre teeth ap- 

 pear worn down. 



Shell close, orbicular, doubly convex, equivalve, sub-equi- 

 lateral ; summits almost vertical, and more or less distant ; 

 hinge formed on each valve by a rather numerous series of 

 small teeth, disposed in a curved line, sometimes broken 

 under the summit ; ligament external and large. 



Pectunculus glycimeris. Pectunculus angulatus 



P. pilosus. P. stellatus. 



P. undulatus. P. pallens. 



P. marmoratus. P. violacescens. 



P. scriptus. P. zonalis. 



