50 
car dine incisuris minidis exasperate. Lister, Conch, tah. 150, 
fig. 5 . 
Encyc. Method, vol. 63 , tah. 249 ,^^. 1 . 
By these dimensions it will appear to vary very considerably, being 
a regular oval ; much elongated ; ovate or nearly orbicular ; some- 
times with two or three longitudinal or oblique waves ; rarely tuber- 
culate y within perlaceous or red purple ; teeth very thick, crenated, 
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 cygnem, 
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 j 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 purpurexjs. — 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, 
fig. 1. 
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, are a little shortened on the base 
opposite to the lamellar teeth. 
Unio ovatus. — Shell subovate, convex, not remarkably thick, 
