72 
PALEONTOLOGY OF NEW YORK. 
obsolescent revolving carina just below, near the upper margin of the 
volution. 
This species has nearly the form of P. sulcomarginata, but the spire is less 
elevated and the volutions more convex, while it is distinctly more concave 
on the lower side. The band of the periphery is scarcely depressed; there is 
no carination above the suture-line, and there are no sharp elevated striae as 
in that species.. The largest specimens seen are half an inch in diameter. 
The relative elevation of the spire in these two species is shown by a compari¬ 
son of figure 21 with figures 9 and 13-16—the latter being much larger shells. 
Fig. 25 is an enlargement of P. rotalia, introduced for comparison with fig. 17, 
a young specimen of P. sulcomarginata , enlarged to the same degree. 
Formation and locality. In the compact shale or calcareous rock of the Ham¬ 
ilton group, at Pratt’s Falls, Madison county, N. Y. 
Pleurotomaria Ella. 
PLATE XX, FIGS. 22-25. 
Pleurotomaria Ella, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 19, figs. 26-29. 1876. 
Shell depressed-trochiform; spire moderately elevated; the entire height 
equal to about four-fifths the greatest width. Volutions four or five, 
depressed-convex on the upper side, gradually enlarging to the outer 
one, which becomes expanded and moderately ventricose towards the 
aperture; lower side gently convex for half its extent, and more rounded 
towards the aperture. Umbilicus closed ; columella apparently not 
extended; periphery somewhat obtusely angular. Aperture transverse, 
subrhomboidal. 
Surface cancellated by revolving and concentric striae,—the former strong, 
defined and continuous, and about eight or ten on the upper side of each 
volution, as shown in the two exterior volutions; these are crenulated by 
the finer transverse or concentric striae, which are usually directed back¬ 
ward, without curving, till close to the peripheral band, where they make 
an abrupt retral curve. The peripheral band is simple, narrow, concave. 
