LAMELLIBRANCHIA TA. 
419 
Panenka equilatera. 
PRATE LXIX, FIG. 4 (7 ?) ; AND PLATE XCIV, FIG. 17. 
Cardiola? equilatera, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 69, fig-. 4. 1S83. 
Shell of medium size, sub-circular; length a little greater than the height, 
Pallial margin regularly rounded. 
Valves convex below, gibbous in the middle and above. 
Hinge-line short. Ligamental area well-defined, not high. 
Beaks sub-central, elevated, turning forward, incurved. 
Surface marked by from forty to fifty simple strong radii with equal inter¬ 
spaces ; radii rarely bifurcating. Also marked by fine, close, concentric 
striae. 
Two specimens measure respectively 34 and 35 mm. in length, and 30 and 
31 mm. in height. 
This species has about the same size and proportions as P. Hero , but the ribs 
are much more numerous and not so strongly elevated. 
Formations and localities. In the Marcellus shales at Avon ; and in the Ham¬ 
ilton group at Pratt’s falls, Onondaga county, N. Y., and doubtfully from Cum¬ 
berland, Md. 
Panenka costata, n. sp. 
PLATE XCIV, FIG. 15. 
Shell large, broad-ovate; length about one-fifth greater than the height. Pal¬ 
lial margin regularly rounded in front and on the base, expanding behind. 
Valves very ventricose in the middle. 
Hinge-line short. 
Beaks sub-central, prominent, incurved. 
Surface concentrically striated, and marked by strong rounded or some¬ 
what flattened costae with narrower interspaces. The radii curve distinctly 
forward on the anterior portion of the shell. Interior unknown. 
One specimen has a length of 51 mm. and a height of 42 mm. 
