382 TESTACKOUS MOBLUSGA. 
or less arcuated; umbones eroded: nacre purple; cardinal teeth 
solid, trigonal, jagged; lateral straight. 1%...24. Mexico. The 
specimen delineated appears an abnormal form, being produced and 
bluntly subcuneiform in front, and very short and convex behind: 
judging from the lines of growth this is not always the case. The 
U. Crocodilorum of Morelet is nearly allied, but the shape is 
oblong, the surface grooved behind, and the teeth less solid and 
triangular. 
Unto coniints (t. 20, f. 57), Conr. Mon. U. t. 36, f. 2. Suboval, 
slightly subtrapeziform when mature, subinequilateral, not solid, at 
most subventricose, not distinctly rayed; when young ochraceous, 
smooth, and armed in the umbonal region with a few short spines 
behind the inconspicuous umbonal ridge; when aged olivaceous- 
brown, unarmed, with concentric wrinkles of increase; ventral edge 
changing from convex to retuse, subparallel with the slightly convex 
front dorsal margin; front extremity broadish, angulated dorsally, 
rounded ventrally; hinder extremity unsymmetrically rounded ; 
wmbones eroded (in the adult), not prominent; nacre tinged with 
flesh-colour; cardinal teeth oblique, 2 in each valve. Pees 
Virginia. 
Unio scopina (t. 23, f. 40), Benson, MS. Oblong, inequilateral, 
moderately thick, rather compressed, with a dark green ray on the 
anterior slope, densely covered with raised corrugations, which, upon 
the simple umbonal slope are disposed #1 somewhat transverse diver- 
gent curved narrow folds, are angularly met beyond it by similar 
raised wrinkles, are arranged upon the hinder extremity in short sub- 
transverse angularly flexuous lines, and elsewhere are broken ito 
short zigzags, or angular dots (like a worn out rasp); dorsal and ven- 
tral edges subparallel, the latter straightish, a little retuse; anterior 
side bluntly biangulated; umbones eroded, not prominent; nacre 
bluish, iridescent in front; anterior lateral tooth elongated, posterior 
lateral tooth very short, much elevated. 7%... 14. Assam. The 
primary tooth in the only valve known to me ts a mere callus. 
Unio RADULA (t. 23, £41), Benson, MS.  'Transversely oboval, 
inequilateral, not very thick, rather compressed, olivaceous, sculptured 
as in U. scobina, but rather more linearly and transversely; ventral 
and front dorsal edges convex and subparallel; hinder extremity 
rounded, narrower: umbonal ridge inconspicuous, umbonal slope 
simple; neither the eroded umbones nor the ligament prominent ; 
nacre bluish; umbonal cavity shallow; hinder tooth strong, compli- 
cated; front lateral tooth elongated, a little curved. 3... Lt. 
Assam. 
Unto cucumor:s (t. 24, f. 4), Lea, Trans. Am. Phil. Soc. 8, t. 7, 
f.2; on U.8, p. 30. Very elongated, subcylindraceous, scarcely 
