OF THE FAMILY OF NAIADES. 407 



be scarcely more unlike than the smooth and radiated *</<- 

 auoideua of Barnes and the beautiful tuberculated locrymo- 

 sus (nobis); and the same remark maybe applied to the 

 eyHndrieus and alahu of that excellent conchologisl Mr Say. 



Many other species could be thus contrasted, hut I deem the 

 above sufficient, upon examination, to prove the justness of 



my remarks, and the necessity, in the present state of our 



knowledge, to retain the species, whatever may be the changes 

 in the genera*. 



In a preceding paper on the Uniones I said something oh 

 the habits of the animal. I wish now to mention the simple 

 fact that I have kept several specimens about ten months in 

 a basin changing the water every five or six days. During 

 this period they passed through the winter without any 

 change in their usual habits, and nothing in the shape of food 

 was given during the whole period. 



This truly interesting family presents us with very diffi- 

 cult specific characteristics, rendered so by the species con- 

 stantly approaching in similitude to each other, and by the 

 change made in them by age, locality, and exposure. 



I propose to offer a few observations on the principal cha- 

 racters, in which it will be seen how little we can depend on 

 any one of them, and shall begin first with the teeth. 



Talk. In the species of the Unio these have been used as 



* In a letter addressed to me by William Cooper, Esq., nn intelligent natu- 

 ralist of New York, he says, " There are now, I think, noi less than thirty North 

 American species of Unio well established, and perhaps Beven or eighl more. 

 That they arc species, each perpetuating iis peculiar form, Bubject t" certain va- 

 riation.--. l)ii t permanent within fixed limits, seems ti the most rational opinion, 



although some of our most judicious naturalists think otherwise Your account 

 of the animal of the I ■ irroratiu affords a strong argument in favour of this belief, 

 for it proves that to be beyond doubt as distinct a apt my in any class of 



animals. Yet this may always be known with certainty by the -In II. which. 

 though -" well characterised, is not, however, more diff< n n( from the n si of the 

 genus, than they are from each other, and frequently -till less so. If. therefore, 

 this difference is found t<> be constantly indicative of a species in one instance, il 

 must also be in others. I believe that our lakes and rivers contained the Baroe 

 form of shells at the creation and ever since thai they do at this day. [fthej are 

 hermaphrodite per se, ns is said of them, it could not be Otherwise : and il the 

 contrary were admitted, natural history would not deserve the name ..| a -cn-ni • 



\ ui,. m. — 5 l 



