163 



hinge sometimes toothless, sometimes with an obscure central 

 tooth or arch , furnished icith a slightly thickened rib -like ful- 

 crum supporting the ligament, which is chiefly internal. 



The curious genus Solemya lias been placed at the head of this family 

 on account of the resemblance of its shell to that of the Siliqna form of 

 Solecurtus on the one hand, and to the shell of Glycimeris on the other. 

 Like the former it is of a thin oblong-square shape, rayed, and rounded at 

 the ends, and the ligament, though chiefly internal, is lodged upon a shelly 

 process, which may be regarded as a modification of the hinge-fulcrum of 

 this and the preceding family. Like the latter it is enveloped by a dark 

 shining-horny epidermis passing over the margin, and the epidermis in 

 this case passes over considerably, and from its curiously brittle nature be- 

 comes much split and jagged. The animal of Solemya has not, however, 

 the sheathed siphons of either of those genera, the mantle having only a 

 simple orifice in front, of which the edges are cirrhated. The foot is, 

 moreover, excavated or funnel-shaped at the extremity, and the animal has 

 been observed to swim about in the water and to make surprising leaps 

 with it, though habitually dwelling imbedded in mud or sand. 



The geographical distribution of Solemya is as anomalous, so far as our 

 knowledge of this bivalve at present goes, as the nature and affinities of its 

 organization. There are four species ; one is a native of the shores of 

 Australia and New Zealand, another inhabits the Mediterranean and West 

 African coast, and the remaining two are found on the shores of the 

 northern United States. 



Species. 



1. Australis, Lam. 3. Mediterranea, Lam. 4. velum, Say. 



2. borealis, Tott. 



Figure. 



Solemya Australis. PI. 44. Fig. 235. Shell, showing its peculiar over- 

 lapping, jagged-edged, shining-horny epidermis. 



Genus 2. GLAUCONOME, Gray. 



Animal; mantle closed except in front for the passage of a small, 

 compressed, tongue-shaped foot ; siphons very long, united 

 nearly to their ends ; orifices fringed. 



