AND OTHER FAMILIES. 175 



extensive dealer in London. He could not give me the least idea of 

 its native country. From its general appearance I should presume it 

 to come from a southern latitude, perhaps from New Holland. It is 

 rather peculiar in its outline, being more emarginate at base than any 

 species with which I am acquainted. The emargination is not, how- 

 ever, so great as in the Mya mar gar it if era (Lin.), Alasmodonta arctiata 

 (Barnes). It approaches most closely the Unio suhtentus (Say), but 

 differs from it in the total absence of folds or " ribs" on the posterior 

 slope. In the two valves which I possess there appear to be no rays, 

 unless the green of the posterior slope be denominated a single broad 

 one. The emargination and compression of the base cause the poste- 

 rior part of the cavity of the shell to be effuse. . 



Unio Conradicus. Plate IX. fig. 23. 



Testd elliptica, transversd, insequilateru, parte posteriori plicatd ; valvuUs tenui- 

 bus ; natibus ad apices nitide undulatis ; deniibus cardinalibus parvis et erectis ; 

 later alibus indistinctis ; margaritd ant ice albd, post ice iridescent e et in cavofusco 

 purpurea. 



Shell elliptical, transverse, inequilateral, folded on the posterior parts ; valves thin ; 

 beaks finely undulated at tip ; cardinal teeth small and erect ; lateral teeth not perfectly 

 defined ; nacre white anteriorly, iridescent posteriorly, and brownish purple in the 

 cavity, 



Hab. . . . , Professor Troost. 



My Cabinet. 



Cabinet of Professor Troost. 



Diam -6, Length -8, Breadth 1*8 inches. 



Shell elliptical, transverse, inequilateral, indistinctly folded on the 

 posterior parts ; substance of the shell thin behind, thicker before ; 

 jjeaks slightly elevated and finely undulated at tip ; ligament rather 

 long and thin ; epidermis finely wrinkled, yellowish brown, with nu- 

 merous indistinct greenish rays, which on the posterior part are dis- 

 posed to be clouded ; cardinal teeth small, erect, disposed to be lobed ; 

 lateral teeth long, slightly curved, not perfectly defined, having but a 

 small cleft in the left valve ; anterior cicatrices distinct ; posterior cica- 



