6 THE AMERICAN MIDLAND NATURALIST z 
margin is slightly rounded.. The surface is smooth and shining 
with coarse lines of growth. The epidermis is yellowish-green and 
distinctly rayed in young specimens, but this color changes to a 
dark brown or even black in old specimens,—in these the rays 
may be. partially or even entirely obliterated. There is a solid 
ligament of a light brown color. The cardinal teeth are double in 
both valves, about equal in size in the left valve, and unequal in 
the right. The lateral teeth are long thin, slightly arcuate and 
smooth. ‘The pallial line is quite distinct. The anterior adductor 
muscle scar is deeply impressed and striated; the posterior 
adductor muscle scar is large, indistinct and confluent. The dorsal 
muscle scar is in the cavity of the beaks and arranged in nearly a 
straight row; there are six or seven small rounded pits, followed 
_by a single long and narrow scar, very deeply impressed. The 
nacre varies from deep purple to salmon pink; iridescent. The 
species may be recognized by the rich purple interior and the more 
or less alate postero-dorsal margin. 
Length 138 Height - 93 Diameter 35 
92 fie! 23 
108 82 30 
LAMPSILIS LEPTODON (Rafinesque). 
Unio (Leptodea) leptodon Rafinesque, Ann. Gen. Sci. Phys. Brux., V, 1820, p* 
296, pl. LXXX, fig. 5-7. 
Unio lepiodon Say, Am. Conch., VI, 1834. 
Symphynota lepiodon Ferrusac, Guer. Mag. 1835, p. 25. 
Lampsilis leptodon Simpson, Syn., 1900, p. 575. 
Anodon purpurascens Swainson, Zool. III., 1st. ser., III, pl. CLX, 1823. 
Unio velum Say, New Harm. Dissem., II, Sept. 23, 1829, p. 293 
Symphynota tenuissima Lea, Tr. Am. Phil. Soc., III, 1829, p. 453, pl. XI, fig. 
21. 
Unto tenuissima Hanley, Biv. Shells, 1843, p. 206, pl. XX, fig. 42. 
This is one of the thinnest shells to be fouud in the St. Joseph 
River. The only sliell that approaches it in appearance is Anodonta, 
the resemblance being in the poorly developed character of the 
teeth. The shell is small, smooth and elongately elliptical in out- 
line. The epidermis varies from a light horn color strongly rayed 
with green in the young specimens, to a dark brown and even 
black color with no rays, in old specimens. The lines of growth 
are inconspicuous except along the ventral margin. The dorsal 
is straight; the anterior margin rounded; the posterior margin 
pointed. The umbones are small and hardly project above the 
