LAMELLIBRANCHIA TA. 
161 
Leiopteria Rafinesquii. 
PLATE XV, FIG. 11 ; PLATE XX, FIGS. 6, 7 ; and PLATE LXXXVIII, FIGS. 27, 28. 
Leiopteria Rafinesquii, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 15, tig-. 11; pi. 20, 
figs. 6, 7. Jan., 1883. 
Shell of medium size, sub-rhomboidal; body rather narrow above, obliquely 
ovate; height equalling or greater than the length; margins regularly 
curved; the post-basal side extended; anterior side sometimes nearly 
straight for a short distance below the ear. 
Left valve convex, gibbous on the umbo. Right valve less gibbous. The 
right valve supposed to belong to this species is convex on the umbo, and of 
moderate convexity below; the height is considerably greater than the 
length, and the body of the valve less distinctly defined than in the left 
valve. 
Hinge-line straight; from the anterior side of the beak to the posterior 
extremity it is about equal to the length of the shell. 
Beak of the left valve acute, directed forward, very prominent, situated 
at the anterior extremity of the shell. Umbonal region gibbous, subtending 
an acute angle. 
Ear short, convex, obtuse, with a broad undefined vertical sulcus and shal¬ 
low byssal sinus. Wing moderately large, flat; margin concave; extremity 
acute. 
Test thin, marked by regular, concentric lines of growth, which are more 
crowded upon the cardinal expansions. The striae are raised at intervals 
into strong, elevated lamellae, which are conspicuous on the cast, and more 
crowded and prominent on the anterior side. The right valve referred to 
this species is marked by concentric wrinkles, which are well-preserved on 
the anterior side, with distant, elevated, lamellose striae on the wing and the 
margin of the hinge. 
Internal characters unknown. The ligamental area appears to be marked 
by a groove along the wing parallel to the hinge-line. 
Three characteristic specimens have respectively the following dimen- 
21 
