AND OTHER FAMILIES. 63 



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 Mija margaritifera (Lin.), Alasmodonta arcuata 

 (Barnes). It approaches most closely the Unio subfenfus (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. 



Testa elliptica, transversd, iitsequilaterd, parte posteriori plicatd ; valvulis tenui- 

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

 later alibus indistinctis ; margaritd antice alba, posiice 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; 

 beaks 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- 



