LAMELLIBRANCHIA TA. 
167 
Ear short, limited by an undefined sulcus and shallow byssal sinus. Wing 
large, triangular, nearly flat, defined by the retral curving of the lamellose 
strise; margin moderately concave; extremity abruptly acute. 
Test thin, marked by regular concentric lines of growth, with distant, 
lamellose striae, which are raised into thin, sharp elevations corresponding 
with the concentric folds or undulations of the shell. The cast shows only 
the undulations. On the anterior margin and wing, the lamellae are closely 
crowded, producing a varicose appearance. They are more closely arranged 
upon the wing than on the valve, making a gentle retral curve and becoming 
very conspicuous on the hinge-margin. 
Interior unknown. Ligamental area narrow. 
A left valve has a length of 46 mm., height 49 mm., hinge-line about 
47 mm. 
This species, in general proportions, resembles A. Bigsbyi; it differs in the 
larger and more extended posterior end, with strife nearly vertical or gently eurv 
ing, except at the hinge margin; the body wider above, and the anterior basal 
margin less convex. With a single t exception, the specimens of L. Bigsbyi 
occur in arenaceous beds, while this species is common both to the softer shales 
and in the coarser beds. 
Formation and localities. In soft shales of the Hamilton group, from loose 
masses of rock at the south end of Seneca lake, and in the coarse grits, at 
Schoharie, N. Y. 
Leiopteria Troosti, n. sp. 
PLATE LXXXVIII, PIGS. 12, 13. 
Shell above the medium size, sub-rhomboidal; body broadly ovate, moderately 
oblique; height somewhat greater than the length; anterior margin, from 
the wing to about half the height, nearly vertical, curving broadly around the 
base, and more abruptly rounded behind. 
Left valve moderately convex, gibbous on the umbo. Right valve unknown. 
Hinge-line straight, somewhat less than the length of the shell. 
