FRESHWATER AND LAND SHELLS. 109 



straight; anterior cicatrices distinct, the smaller being situated above 

 the large one; posterior cicatrices confluent; dorsal cicatrices very 

 small; cavity of the shell rather deep; cavity of the beaks shallow. 



Remarks. — This shell belongs to Lamarck's genus Hyria^ which, in 

 my proposed arrangement, I have placed among the Uniones having 

 one cardinal and one lateral tooth. I am induced to believe in the 

 propriety of this remaining so, until we shall have a better knowledge 

 of the whole family, and of course a natural arrangement. In a pre- 

 vious memoir* I noticed the fact, that in the genus Hyria the cicatrix 

 of the extensor muscle was placed over that of the anterior adductor 

 muscle. In the Brownianus we find them in the same relative posi- 

 tion. 



I am indebted to Captain Brown for the examination of three spe- 

 cimens of this species, which he brought from the Amazon, with the 

 other two species already known to exist there. It most resembles H. 

 syrmatophora, but diflfers from it in being more transverse, being less 

 carinate, having a shorter cardinal tooth, which is more striate, and in 

 having a wing much less elevated. The umbones are also more infla- 

 ted before the umbonial slope. It may be proper to remark here, that 

 in some individuals of the genus Hyria an imperfect crenulation of 

 the lateral tooth may be found, somewhat similar to the genus Casta- 

 lia (Lam.), and this is the case with one of the specimens of the spe- 

 cies proposed above. 



* Vol. IV., p. 67. 



VI. — 2 c 



