﻿I.AMPSIUS 125 



Both male and female shells are wider behind, but the male 

 shell is somewhat rhomboid, the somewhat biang-ulate posterior 

 point being- near the base of the shell. The posterior end of 

 the female shell is usually faintly biangulate, but it is placed 

 rather hig-her than in the male and the post-basal swelling is 

 but feebly developed. The female shell is higher than that of 

 the male. 



Length (male) 42, height 2^, diam. 16 mm. 



Length (femiale) 42, height 30, diam. 16 mm. 



Type locality, Coosa River at Wetumpka, Alabama. 

 Unio plancus Lea, Pr. Ac, N. Sci. Phila., IV, i8fx), p. 307; Jl. 



Ac. N. Sci. Phila., V, 1862, p. 81, pi. x, fig. 229; Obs., VIH, 



1862, p. 85, pi. X, fig. 229. 

 Margaron (Unio) plancus Li;a, Syn., 1870, p. 50. 

 Lampsilis plancus Simpson, Syn., 1900, p. 556. 

 Unio difficilis Lea, Pr. Ac. N. Sci. Phila., XK, 1868, p. 144; Jl. 



Ac. N. Sci. Phila., VI, 1869, p. 31 1, pi. xlix, fig. 124; Obs., 



XII, 1869, p. 71, pi. XLix, fig. 124. 

 Margaron (Unio) difficilis Lea, Syn., 1870, p. 46. 



I am doubtful whether this is more than a rather short, some- 

 what rhomboid variety of L. nebulosa with a well-developed 

 [Kisterior ridge. The female shell, however, seems to differ in 

 shape from that of nebulosa. 



(iroup of Lampsilis subangulata. 



Shell elliptical, inflated, subsohd, drawn to a point behind ; 

 that of the female only slightly swollen just behind the central 

 base ; bars of the beak sculpture somewhat coarse, feebly double 

 looped ; epidermis very smooth, shining, brightly rayed ; teeth 

 rather smooth, subcompressed ; nacre bluish or purplis'h. Ani- 

 mal having the marsupium very large ; ovisacs numerous ; gills 

 large, nearly semicircular. 



Lampsilis subangulata (Lea). 



Shell long elliptical or long ovate, rather solid, subinflated, 

 with full, but not high, beaks, the sculpture not seen; posterior 

 ridge well developed, slightly rau^lded ; anterior end round ; 



