42 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



PLEUROTOMARIA AKATA ( n.s.). Hs j^ ^ /^/^ 

 Shell depressed suborbicular. Spire moderately elevated : volutions 

 three or four, gradually enlarging, the outer half of the body- 

 Volution being ventricose. Aperture somewhat transverse. m 

 Surface marked by strong distant angular ridge-like strise parallel 

 to the finer lines of growth; a strong band marking the periphery 

 of the shell. 



This species is abundant in the Schoharie grit, in the condition of casts 

 of the interior : individuals are rarely found, retaining the shell in greater 

 or less perfection ; and some of the stronger markings are not unfrequently 

 preserved on the casts, or as impressions of the exterior upon the surround- 

 ing matrix. The diameter of the shell is from one inch to two and a quarter 

 inches, and the vertical height in the largest specimens is about an inch and 

 a quarter. The shell appears to have been distinctly umbilicate. 



Geological formatio7i and locality. In the Schoharie grit : Helderberg 

 mountains and Schoharie. 



PLEUROTOMARIA LUCINA ( n. s.). iPm^J ^'^ 



Euotn-phalus? rotundus : Geol. Report 4th District New-York, 1843, p. 172, f. 4. 

 ot Pleurotomaria rotundata of Muxster. / i< .. ^ 



Shell suborbicular. Spire elevated : volutions about four; apex 

 minute. Volutions gradually expanding to the last one, which 

 becomes very regularly ventricose, with the aperture expanded 

 and nearly round, or 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 canalicu- 

 late. Lower side of the body-volution convex in the middle, and 

 gradually depressed into the umbilicus. 



Surface beautifully cancellated by concentric and revolving strise, 

 which, in many specimens, are of equal strength. Periphery 

 marked by a moderately wide band, on which the strise are 

 turned abruptly backwards : this band is limited by stronger 

 strise or narrow ridges, and sometimes one or two slender re- 

 volving strise are within the extent of the band. 



This species is well marked by its symmetrically rotund form 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 

 which appear all to belong to this species. The concentric* striae are some- 



[ August, 



