Fragments of Natural History. 



165 



Lea. 



This view of the subject has, I believe, borne the test of ex- 

 amination, at least in our own country ; for, so far as I am in- 

 formed, it is sustained by every American naturalist who has had 

 opportunities for carefnl and extensive observation. It holds true 

 in respect to the following species found in the waters of the 

 western states, the animals of which I have repeatedly dissected 

 at different seasons of the year, and under various circumstances 

 and conditions, without finding in any instance an exception — 

 to wit : 



Unio ^sopus of Green. 

 alatus " Say. 



lapellus " " 

 nasutus " " 

 ovatus " " 



compressus '' 

 capsasformis 

 circulus " 

 iris " 



irroratus ". 

 lasvissimus " 

 multiplicatus 

 multiradiatus 

 pileus* " 



In several of the above species, the difference in the outlines of 

 the shells in the two sexes is slight, and might escape the atten- 

 tion of a hasty observer, yet it is permanent and invariable la 

 whatever locality they are found. 



There are certain other species in which the sex is not attend- 

 ed with any corresponding difference in the shell, at least so far 

 as I have been able to discover. It may however yet be found 

 upon further examination, that some minute difference has been 

 overlooked. Of this character are the following: 



* The pileiis of Lea, and ihe -personatus of Say, are the male and female of the 

 same species. 



t The female is the U. velum of Say. 



t The U. donaciformis, is the female of this species. 



§ The Margaritana deltoidea of Lea is the male, varied from the asual form and 

 size by the peculiar influence of the waters of Mill Creek, near Cincinnati. 



