12 PALJCONTOLOOV OF NEAV-YORK. 



393. 19. PLEUROTOMARIA? PERVETUSTA. 



Pt.. IV. (bis). FiRs. 3 a, b, c, <1. 



Cydostoma pervelusta. Coniiau, Annual Report 1838, y>. 113; 1839, p. 65. 

 PleurJtomaria pervetusta. Hall, (ieol. Report 4tli District, 1843, pag. 48, figs. 1 & 2. 



Shell suborblculiir or depressed-conical ; volutions about four, gradually enlarging ; umbilicus 

 large, extending to the apex ; surface of the cast smooth. 



This little shell is found in immense numbers, as if it had been drifted together by waves or 

 currents ; but 1 have never been able to find one in which the m'-irkings of the surface are 

 preserved. It is either in the condition of casts in the weathered portion of the rock, or in the 

 solid portions having the shell crystalline, so that all surface characters are obliterated. Under 

 these circumstances, I have referred it to the Genus Pleurotomaria. In its character and habits 

 it is much like Littorina, but it is associated in great numbers with the Lhigula cuneata. its 

 almost uniform size is that of the specimens figured, and many thousands often occur in the 

 space of a few feet. 



Fig. 3 a. Profile view of a specimen. 

 Fig. 3 J. View of the base. 

 Fig. 3 c. View of the apex. 



Fig. 3 <Z. A fragment of the sandstone containing numerous individuals of this species, with 

 Bucania trilohata. 



Position and Incnlity, This species is exceedingly abundant at Medina, constituting by itself, 

 and with the Lingula cuneata, some thin beds about sixty feet below the surface of the rock. 

 It occurs more rarely at Lockport. (State Collection.) 



394. 20. PLEUROTOMARIA LITOREA(n.s;).). 



Pl. IV. (bis). Fig. 4 a, b. 



Subconical volutions about 3 or 4, somewhat obtusely angular, rapidly enlarging ; mnbilicus 

 small ; surface markings unknown. 



Two specimens, both casts, of this spec-ies have been found. It differs from the last in its 

 greater size and more rapidly ascending spire. The umbilicus is also much smaller, and it will 

 not readily be confounded with that species. The specimen figured seems somewhat depressed 

 from pressure, and its height is less than another specimen, 



Fig. 4 a. Profile view of specimen, Fig. 4 b. View of the apex. 



Position and locality. This species occurs at Lockport, irj the upper part of the rock. I am 

 indebted to Col. .Ikwett for the specimen figured. 



