6 
PALEONTOLOGY OF NEW YORK. 
Aviculopecten Cleon. 
PLATE I, FIG. 1. 
Aviculopecten Cleon, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 1, tig. 1. Jan., 1883. 
Compare with the young of A. princeps. 
Shell small, ovate; transverse axis slightly oblique; length somewhat greater 
than the height; margins regularly rounded. 
Left valve convex, the convexity equal to about one-sixth the length of 
the hinge-line. The point of greatest convexity is just anterior to the 
centre of the shell and towards the beak. Right valve not observed. 
Hinge-line straight, length five-sixths the height of the entire shell. 
Beak anterior to the middle of the hinge, not prominent-. 
Ears defined by the absence of radiating lines, but not by any marked 
change in the convexity of the shell; lateral margins concave. The anterior 
ear is limited by a shallow groove. The posterior ear is about twice the 
size of the anterior. 
Test thin, ornamented by a reticulation of fine radiating lines, and finer 
concentric striae of growth. The stronger rays have one or two finer lines 
between. The lines of growth extend over the ears, but less distinctly than 
over the body of the shell; and otherwise the ears are nearly smooth. 
Interior not observed in the specimen described. 
The length of this specimen is 21 mm., height 24 mm., hinge-line 20 mm. 
This form resembles the young of A. princeps, but it is less oblique, and the 
ears less strongly defined than in the young of that species as represented in 
authentic specimens. The figure does not quite represent the form of the 
specimen, and the posterior ear is not so well defined as is shown in the 
illustration. The form A. exacutus is very similar to this one; but that species 
has fewer and sharper radiating striae, and the geological horizons of the two 
are widely separated. 
Formation and locality. Upper Helderberg limestone, Columbus, Ohio. 
