50 



car dine incisuris mnmlis exasperate . Lister, Conch, tab. 150, 

 Jig. 5. 



Unc7/c. Method, vol 63, tab. 249, Jig. 1. 



By these dimensions it will appear to vary veiy considerably, beiag 

 a regular oval ; mucli elongated ; ovate or nearly orbicular ; sone- 

 times with two or three longitudinal or oblique waves ; rarely tuler- 

 culate; within perlaceous or red purple; teeth very thick, crenaied, 

 and resembling those of the next species. It is very probable that 

 we have here included several distinct species, but at present we 

 are not sufficiently well acquainted with the inhabitants to separate 

 them. Gmelin refers to Lister's figure for his Mytillus a/gneus, 

 but we can discover no resemblance between them. 



Found plentifully in the river Ohio and its tributary streams. 

 Unio plicata. — Shell suboval, thick and ponderous; valves 

 with two three more conspicuous undulations, which are profound, 

 very oblique, continued to the anterior basal edge, and not arising 

 from the umbo ; umbo decorticated, sometimes much eroded ; 

 within perlaceous, distinctly impressed by the undulations. 



This species may be distinguished from any of the numerous 

 varieties of the preceding species by the oblique direction of the 

 undulations, of which those nearest the base are largest, and seem 

 to originate behind the beaks. 



It was found by Mr. Lesueur in Lake Erie, and was communicated 

 by him under the above name. 



Unio purpureus. — Shell suboval, somewhat compressed, with 

 smaller wrinkles placed between larger ones, color dark brown ; 

 beaks placed nearer one end, very carious, not prominent, generally 

 the epidermis and pearly strata are removed, exhibiting a wax-yel- 

 low ground ; within reddish purple, varied with green, no cavity 

 under the beak; teeth resemble the preceding. Length, one inch 

 and five-eighths; breadth, two inches and four-fifths. Plate 3, 

 figl- 



This species is more numerous in the rivers Delaware and Schuyl- 

 kill than any other of the genus : in the rivers of the Southern 

 States it arrives at a more considerable magnitude, measuring some- 

 times four inches, or more, in breadth. These large specimens, 

 and sometimes the smaller ones, arc a little shortened on the base 

 opposite to thd lamellar teeth. 



Unio ovatus. — Shell subovate, convex, not remarkably thick, 



