UNIO 613 
and one lateral; beak cavities moderate; muscle scars small, 
shallow ; nacre creamy white, thicker in front. 
Length 39, height 24, diam. 15 mm. 
South Carolina. 
Type locality, Abbeville District, S. C. 
Unio merus Lea, Tr. Am. Phil. Soc., X, 1852, p. 260, pl. xv, 
fig. 10; Obs., V, 1852, p. 16, pl. xv, fig. 10—Srmpson, Syn., 
1900, p. 708. 
Margaron (Unio) merus Lea, Syn., 1870, p. 54. 
Unio castus Lea, Pr. Ac. N. Sci. Phila., IV, 1860, p. 306; JI. 
HEN. set Phila, TV; 1860,-p. 340, pl..ivil, fig. 1745°Obs., 
VIII, 1860, p. 31, pl. wit, fig. 174. 
Margaron (Unio) castus Lea, Syn., 1870, p. 40. 
Close to forms of pusillus and perhaps only a variety of it. 
The posterior ridge is single in all the shells I have seen; it is 
heavier and more distinctly rhomboid than that species. The 
posterior slope is without wrinkles in all the examples I have 
seen, and is very feebly radially furrowed. 
Unio mMasont Conrad. 
Shell small, somewhat rhomboid, though rounded above, in 
front and below, slightly inequilateral, subcompressed ; beaks 
moderately full but not much elevated, their sculpture not 
known; posterior ridge well developed, angled, ending behind 
just above the base ; epidermis olive, clouded with brown, shin- 
ing; pseudocardinals prominent, compressed, oblique; beak 
cavities capacious ; nacre bluish-white. 
Length of the figure 26, height 20 mm. 
Type locality, Savannah River, Augusta, Ga. 
Unio masoni Conrap, New F. W. Shells, 1834, p. 34, pl. v, 
fig. 2; Monog., III, 1836, p. 28, pl. xu, fig. 2—HAN Ley, Biv. 
Shells, 1843, p. 201, pl. xxi, fig. 18.—CHENU, Bib. Conch., 
tst ser., IIT, 1845, p. 18, pl. u, fig. 1—Kuster, Conch. Cab. 
Unio, 1852, p. 34, pl. v, fig. 6—SIMPSON, Syn., 1900, p. 709. 
Margarita (Unio) masoni Lea, Syn., 1836, p. 33; 1838, p. 23- 
‘Margaron (Unio) masoni Lea, Syn., 1852, p- 34: 1870, p. 55. 
