44 CONCHOLOGY. 



groove divided in the middle of the margin, ligament internal 

 inserted in a pit. Tv^ro species. 



Ungulina oblonga. Ungulina transversa. 



6. Genus Solemya. PI. VI. 



Animal. Unknown. 



Shell. Covered with a thick epidermis, enclosing it entirely 

 except at the extremities, regular, somewhat thick, oval, elongated, 

 straight and parallel edges, also rounded at its two extremities, 

 valves equal, very inequilateral ; the anterior side much longer 

 than the posterior ; summits feebly marked ; hinge subsimilar, 

 formed by a cardinal tooth, dilated, compressed, and a little reflexed 

 above ; subexterior ligament inserted upon the tooth, and nearly 

 at the posterior extremity of the shell ; two small, rounded, widely 

 separated muscular impressions, without any visible abdominal 

 Impression. Four species. 



Solemya Australis. Solemya Mediterranea. 



S. velum.* S. borealis.* 



7. Genus Amphidesma. PI. VI. 



Animal. Very imperfectly known. 



Shell. Transverse, inequilateral, somewhat rounded or sub- 

 oval ; sides slightly gaping ; hinge with one or two cardinal teeth, 

 and a narrow groove for the internal ligament; ligament double, 

 the external one short, the internal one fixed in the internal 

 grooves. The two ligaments distinguish this genus from all other 

 bivalves. Inhabits the West Indian and American seas. Forty- 

 live species. 



Amphidesma variegatum. Amphidesma Tenuii. 



A. donacillum. A. purpurescens. 



A. lacteum. A. nucleolum. 



A. corneum. A. physioides. 



A. albellum. A. pulchrum. 



A. flexuosum. A. pallidum. 



A. prismaticum. A. formosum. 



A. phaseolinum. A. roseum. 



