UNIO 553 
en up, and which extend well out on the disk, but begin at 
the beaks as normal, somewhat coarse Unio sculpture, some- 
times with fine radial lines posteriorly ; pseudocardinals, rather 
solid, subcompressed, smooth below ; laterals straight or slight- 
ly curved; cavity of the beaks rather deep; muscle scars dis- 
tinct. 
I have never seen the soft parts of any member of this 
group. Quite a number of descriptions have been published 
of various nominal species, most of which go into details as to 
the color of the different parts, but do not give an atom of 
information as.to real characters. ‘The animal is dark or high- 
ly colored, and seems to be gravid in summer, and no doubt 
carries the voung in the outer gills alone. Gills large, wider 
behind, inner the larger, especially in front; mantle thickened 
at the edges ; palpi very large, elliptical, rounded behind, hang- 
ing at an angle of 45°; branchial opening large, strongly 
fringed. 
UNIO LITTORALIS Lamarck. 
Shell generally subrhomboid, subsolid to solid, subcompress- 
ed to convex, somewhat inequilateral; beaks full and elevated, 
their sculpture consisting of numerous broken ridges, which 
have often a tendency to become doubly looped. This sculp- 
ture quite commonly assumes the appearance of a checkerboard 
and extends well out on to the disk; posterior ridge well de- 
veloped, single or faintly double, ending behind near the base 
of the shell; surface rather rough, the incremental sculpture 
irregular, rarely feebly tuberculate; epidermis varying from 
dirty yellow-green in the young to black in old shells; in the 
lighter colored shells sometimes faintly rayed; left valve with 
two pseudocardinals, the anterior compressed, occasionally 
joining the triangular posterior one; right valve with one 
pseudocardinal, with sometimes a vestigial one in front of and 
behind it; sometimes the pseudocardinals are all heavy and 
much torn; there are two straight or curved laterals in the 
