140 
dull yellowisli brown ; umbo much eroded, exhibiting a chalky 
white stratum, then a dull wax yellow surface ; beak a little 
undulated, hardly elevated above the general curvature ; hinge 
margin forming a large angle with the base, being anteriorly ele- 
vated into an obtuse angle, whence the edge descends almost recti- 
linearly to the anterior margin, which is equally rounded with the 
posterior margin. 
Length one inch and three-tenths ; breadth less than two inches. 
Convexity less than seven-tenths. Inhabits Mexico. 
I obtained several specimens in a ditch beside the road betwee® 
the Capitol and Tacubya. It is perfectly distinct from any 
species of this country that I have seen. It cannot be the 
A. glauca, Lam., as that shell is represented to have Natihiis 
prominuMsJ^ 
Anodonta imbecilis. — Transversely oblong subovate, very 
thin and fragile ] disks convex, green, with darker green obsolete 
rays, and three obvious rays on and above the umbonial slope ; 
hinge margin rectilinear, terminating before in an angle ; beaks a 
little undulated and not elevated above the general curvature ; 
from the anterior tip of the hinge margin the slope is rectilinear 
to the anterior margin ; within bluish white, iridescent before ; 
hinge perfectly rectilinear ] posterior margin rounded. 
Length, over one inch. Breadth, over two inches. Convexity, 
three-fifths of an inch. Inhabits Wabash Biver. 
By these dimensions, it is evident that the present species is 
proportionally broader than any other of our Anodontse. of the same 
length. It does not appear to be common in this river, or it may 
have been overlooked or rejected as a young JJnio by our collec- 
tors, without examination. On this account, perhaps, I have only 
two specimens, of which the smaller is less than half the size of 
the present. It may be a young shell, but if so, in the adult 
state it must be much elongated, inasmuch as its proportions are 
now nearly those of the full grown cygnea, Linn. It cannot be 
the elongata, Swainson, as the shape differs, and that is a thick 
shell with prominent umbones. 
Melania pluristriata. — Turreted; with numerous trans- 
verse, elevated lines. 
Inhabits Mexico. 
