44 CONCHOLOGY. 
groove divided in the middle of the margin, ligament internal 
inserted in a pit. Two species. 
Ungulina oblonga. Ungulina transversa. 
6. Genus Solemya. Pl. 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. Pl. 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- 
five 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. 
