GASTEROPODA. 
67 
Pleurotomaria Lucina. 
PLATE XVIII, FIGS. 1-11. 
Euomplialus? rotundus, Hall. Geology of N. Y. Surv. Fourth Geolog. Dist., p. 172, f. 4. 1843 
Not Pleurotomaria rotundata, Munster. 
Pleurotomaria Lucina , Hall. Descriptions of New Species of Fossils, etc., p. 14. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 42, pi. 5, f. 12. 1862. 
“ rotunda and P. Lucina , Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 18. 1876. 
Shell subglobose, or obliquely ovoid-conical. Spire moderately elevated ; apex 
minute. Volutions about four, gradually expanding to the last one, which 
becomes very regularly ventricose, with the aperture expanded and nearly 
round, extended on the lower side, with a shallow notch on the anterior 
margin; upper side of the volutions very symmetrically convex; suture 
neatly defined, slightly canaliculate; lower side of the body-volution 
convex in the middle, and abruptly curving into the umbilical depression. 
Surface beautifully cancellated by concentric and revolving striae, which, in 
many specimens, are of equal strength. Periphery marked by a mod¬ 
erately wide band, on which the striae are turned abruptly backwards; 
this band is limited by stronger striae or narrow ridges on each side, 
sometimes with one or two slender revolving striae within the limits of 
the band, marking a narrower space, which is often crenulated by the 
concentric striae. 
This species is well marked by its symmetrically rotund form, with moderate 
elevation of the spire, and the regular convexity of the volutions, even in casts 
of the interior, when not compressed. There is some variety in the surface 
markings of specimens apparently belonging to this species. The concentric 
striae are sometimes much coarser than the revolving ones; and finer striae are 
implanted between the stronger ones, and do not reach the suture-line. In old 
individuals the revolving band is sometimes nearly a quarter of an inch in width. 
A very symmetrical specimen has a diameter of a little more than two inches, 
and is nearly an inch and three-fourths in height. Another specimen, which 
has suffered some compression, has a breadth of about three inches, with nearly 
the same height of spire. 
