LAMELLIBRANCHIA TA. 
341 
specimen, is partially exposed, showing the characteristic crenulations of the 
hinge. 
The specimen described has a length of 51 mm. and a height of 30 mm. 
The nearest relation of this form is with P. permana, but it is a, much larger 
shell and its general form more distinctly elliptical. The surface markings on 
the posterior part of the shell are precisely similar to that species, but the 
specimen described is a cast, and an exact comparison cannot be drawn. 
Formation and locality. In the Hamilton group, at Patterson’s creek, Va. 
Pal^eoneilo arata. 
PLATE L, FIG. 23. 
Palceoneilo arata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 50, tig-. 23. 18S3. 
Shell of medium size, sub-elliptical; length about twice the height; basal 
margin convex in the anterior half, concave posteriorly, and rather abruptly 
recurving. Posterior extremity somewhat prolonged and abruptly rounded. 
Cardinal line nearly straight or slightly arcuate. Anterior end regularly 
rounded. 
Valves moderately convex, gibbous in the umbonal region. 
Beaks between the anterior third and fourth, not prominent. Umbonal 
slope convex, without defined ridge, merging in the general convexity before 
reaching the posterior extremity. Post-cardinal slope concave, constricting 
the margin of the shell. 
Surface marked by extremely fine concentric striae, which are often obscure 
or obsolete, and by distant, strong, elevated, lamellose ridges. Interior 
unknown. 
The specimen described has a length of 30 mm. and a height of 16.5 mm. 
This species somewhat resembles P. tmuistriata and P. fecunda , but there is 
an entire absence of an umbonal ridge, or interruption in the curvature of the 
posterior part of the shell, and the lamelliform ridges are stronger and more 
distant. 
44 
