588 UNIO 
darker and wrinkled on the posterior slope; pseudocardinais 
small, double in both valves; laterals heavy, long, and curved; 
muscle scars rather deep; beak cavities small and angular; 
nacre white and iridescent. 
Length 57, height 35, diam. 23 mm. 
Said to come from the Ohio Canal below Columbus. I am 
sure that the locality is wrong, and it appears to be a Mexican 
form. 
Unio callosus Lea, Pr. Am. Phil. Soc. II, 1841, p. 31; Tr. Am. 
Phil. Soc. VII: 1842,. p. 230, plo xxi, tie. 254 Obane las 
1842, p. 77, pl. xx1u, fig. 54.—CHENU, Ill. Conch., 1858, pl. 
XXVI, figs. 4, 4a, 4b.—Simpson, Syn., 1900, p. 701. 
Margaron (Unio) callosus Lea, Syn., 1852, p. 33; 1870, p. 33. 
I cannot believe it possible that the shell Lea described, 
which belonged to Dr. Jay, came from the Ohio Canal 12 
miles below Columbus. The region around Columbus, Ohio, 
has been as thoroughly collected out perhaps as any in the 
United States and nothing like this shell has ever been found 
there so far as I know. It seems to me to be very closely 
allied to U. coloratus Charpentier, if not absolutely identical 
with it, and it is in all probability a Mexican species. 
Unio MEXICANUS Philippi. 
Shell rhomboid, rather solid subinflated, its greatest diame- 
ter being considerably behind the beaks, with a rather strong 
rounded posterior ridge; beaks high, somewhat full, their sculp- 
ture not observed ; epidermis fuscous ; pseudocardinals strong ; 
laterals elongated, nearly straight; nacre purple and shining. 
Length 64, height 37, diam. 23 mm. 
Mexico. 
Unio mexicanus Purr, Zeits. fir Mal., IV, 1847, p. 95.— 
Putter, Abbild. und Beschr., III, 1849, p. 110, pl. v1, fig. 3. 
—Kuster, Conch. Cab. Unio, 1862, p. 285, pl. xcv, fig. 7.— 
SIMPSON, Syn., 1900, p. 7OI. 
Margaron (Unio) mexicanus Lea, Syn., 1870, p. 53- 
Philippi gives a miserable colored figure of this species, 
which is so blurred that it is almost useless for purposes of 
