OF THE FAMILY or \\I\MI>. II j 



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

 generally will be found on the under pait of the cardinal 

 tooth. Sometimes six or eighl may be found ; and their di- 

 rection is towards the lamellar tooth. In thin shells tl 

 cicatrices will be found in the cavity of the beak-, 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 it' the specimen be 

 elongated and thin: and it may he short and thick if it be pon- 

 derous and obtuse. Thus Ave may find in an elongated sili- 

 quoukus 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 <in the 

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

 diffidence give the results, hoping my views may no! be found 

 to be incorrect. 



The first column contains the species, the nomenclature 

 of which i^ now likely to be permanent and fixed. The 

 cond the species described by other writers, which are eitl 

 tin same or varieties, and consequently synonymes. 



Lam. 

 I. U. radiattnf , Gmelin, rirginiana, Lam. 



( l . radiata, 



J. rirginiana, 

 t ;. radiata*, 



Barnes. 



* Sec my description of new LJniones in this volunfe. 



t Lister (t. 162, f. 7.) g trrect representation of the species known to 



American conchologists as U. radiatvs, ami which hi itne Prom ^ i 



Chemnitz (vol. vi. t. j, f. 7.) gives i representation of a shell yeiy similar ' 



the locality of which is Malabar. The tir-t ni ■ »>■ find foi Om 



M'jn radiata, and this author refers to both figures in hisd< scription. Dills 

 VOL. III. 5 N 



