170 
PALEONTOLOGY OF NEW YORK. 
Beaks acute, prominent, directed forward, anterior to the middle of the 
shell. Umbonal region gibbous, subtending an acute angle. 
Ear small, straight on the upper margin; marked by an oblique fold, and 
separated from the body by an abrupt sulcus and a well-defined byssal sinus. 
Wing small, triangular, joining the body of the shell below the middle of 
its height, defined by a change in the direction of the surface striae; margin 
gently concave ; extremity acute. 
Test thin, marked by fine concentric striae, and at regular intervals by 
stronger elevated striae, which give to the macerated shell, and the cast of the 
interior, a regular banded surface. These stronger striae are closely arranged 
on the anterior side and ear, while on the posterior side they preserve their 
equidistant character. The right valve is very distinctly marked by the 
elevated concentric striae. In both valves there are radiating lines which 
apparently belong to the structure of the shell. 
Interior unknown. Ligamental area narrow. 
One specimen has a length of 13 mm., height 16 mm., hinge-line about 
10 mm. Another example has a length of 12 mm., height 13 mm., and 
hinge-line about 11 mm. 
The small size, erect ovate form, short hinge-line, the proportions of height 
and length, and the surface characters, distinguish this species from every other 
form here described. 
Formation and localities. In the soft shales of the Hamilton group; shores of 
Canandaigua lake, and at Norton’s Landing, Cayuga lake, N. Y. 
Leiopteria Oweni. 
PLATE XX, FIG. 10. 
Leiopteria Oweni, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 20, fig. 10. Jan., 1883. 
Shell quite large, sub-rhomboidal; body broadly ovate, oblique to the hinge¬ 
line; length greater than the height; margins rounded, produced posteriorly. 
Left valve convex, umbo gibbous, beak elevated. Bight valve concave 
