OF THE FAMILY OF NAIADES. 415 



ment of the superior part of the mantle in ponderous shells, 

 generally will be found on the under part of the cardinal 

 tooth. Sometimes six or eight may he found ; and their di- 

 rection is towards the lamellar tooth. In thin shells these 

 cicatrices will he found in the cavity of the beaks, generally 

 traversing it in an oblique direction*. 



Ligament. This part of the shell must be viewed with 

 the same doubt as the above character. In the same species 

 the ligament may be long and narrow if the specimen be 

 elongated and thin ; and it may be short and thick if it be pon- 

 derous and obtuse. Thus we may find in an elongated sUi- 

 quoideus the ligament an inch and a quarter long, and only 

 one-tenth of an inch broad, while in an obtuse and ponder- 

 ous specimen it may be found to be only three quarters of an 

 inch long and yet one-eighth of an inch broad, as is the case 

 in some specimens of my cabinet. 



It has been a desideratum with the American concholo- 

 gists to fix the nomenclature of this interesting genus, parti- 

 cularly so far as relates to our own species. In the hope of 

 contributing in some measure to so desirable an object, I 

 have carefully examined all that has been published on the 

 subject so far as I could procure the descriptions, and with 

 diffidence give the results, hoping my views may not be found 

 to be incorrect. 



The first column contains the species, the nomenclature 

 of which is now likely to be permanent and fixed. The se- 

 cond the species described by other writers, which are either 

 the same or varieties, and consequently synonymes. 



1. U. radiatusf, Gmelln, 



* See my description of new Uniones in this volume. 



t Lister (t. 152, f. 7.) gives a correct representation of the species known to 

 American conchologists as U. radiaius^ and which he says came from Virginia. 

 Chemnitz (vol. vi. t. 2, f. 7.) gives a representation of a shell very similar to it, 

 the locality of which is Malabar. The first name we find for it is in Gmclin, 

 Mya radiata, and this author refers to both figures in his description. Dillwyn re- 

 VOL. III. 5 N 



