GASTEROPODA. , 57 



Pleurotomaria Lucina. 



PLATE XVIII, FIGS. 1-H. 



JEaomphalanf rotundiis. Hall. Geology of N. Y. Surv. Fourth Geolog. Dist., p. 172, f. 4. 1843 



Not Pleurotomaria rotundata, Monster. 



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 strke 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. 



