60 
PALEONTOLOGY OF NEW YORK. 
Pleurotomaria plena. 
PLATE XVII, PIGS. 11, 12, 13. 
Pleurotomaria plena, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 17. 1876. 
Shell ovoid-conical, rotund; spire elevated; apex minute. Volutions five or 
six, gradually expanding, rounded above, and somewhat abruptly curving 
downward at the sides, the last one becoming very ventpicose. The 
periphery along the line of the band is apparently a little project¬ 
ing beyond the regular curve of the volution; lower side very convex 
in the middle, and thence abruptly curving inward to the umbilical region. 
Surface marked by somewhat coarse, regular striae, about equal to the spaces 
between, which are directed gently backward from the suture almost to 
the limit of the peripheral band, being abruptly deflected at the junction. 
The peripheral band is crossed by abruptly curving striae, and, on the 
volutions preceding the last one, scarcely rises above the suture-line. No 
revolving striae have been observed upon the body of the shell, though in 
better preserved specimens they may exist. 
This species, in general form, differs from P. Lucina in that it is a more 
erect shell, the spire is more elevated, and the volutions more gradually 
expanding, while the latter presents a slight difference in its rotundity, and, 
in the same way, a scarcely describable difference in the convexity of the 
higher volutions; it has also the two sets of striae almost equally conspicuous. 
From the forms of P. arata known, P. plena differs in the greater elevation of 
the spire, and the finer concentric striae, of which there are twice as many in 
a given space. 
The shell is imperfectly preserved in the specimen figured, and the peripheral 
band is much obscured, especially on the higher volutions. The peristome is 
broken away to a considerable extent, and the form of the aperture can only 
be inferred from a section of the volution, which is subcircular and slightly 
transverse. 
Formation and locality. In limestone of the Upper Helderberg group, Helder- 
berg mountains, Albany county, N. Y. 
