CONTRIBUTIONS TO PALiEONTOLOGT. 45 



.01^. f,U 



PLEUROTOMARIA C APILLARI A (Conrad). ^^ ^// 



Pleurotomaria capillaria : Conrad, Jour. Acad. Nat, Sciences, Philadelphia, 1842, 



Vol.viii, pa. 271, pi. 16, f.ll. 



" Turrited volutions slightly angulated below the middle, with 

 " spiral carinated lines; the second and third lines from the 

 " suture, on the upper part of the volutions, more distant from 

 " each other than from the adjoining striae : upper part of the 

 " volutions very obliquely rectilinear. Surface with equal sharp 

 " lines which cross the volutions obliquely." 



In the coarser shales of the Hamilton group, there is a species of Pleu- 

 rotomaria corresponding to the figure given by Mr. Conrad. The inter- 

 mediate revolving strisD on the upper side of the volution are faintly defined, 

 and may become obsolete : the volution is a little flattened upon the upper 

 side, with a prominent band upon the periphery. 



In the limestone of the Upper Helderberg, below the Hamilton group, 

 there are specimens of Pleurotomaria of nearly the same form and cha- 

 racter as those here mentioned in the Hamilton group ; but the species is 

 more slender and the body-whorl is proportionally more ventricose than 

 those in the Hamilton group, and the concentric striae are much more closely 

 arranged. This variation may be due to difi"erence of physical conditions, and 

 not be of specific importance. 



Geological formation and locality. In the Hamilton group at Cazenovia 

 and Skeneateles, etc. 



PLEUROTOMARIA TRILIX (n.s.). ^^ ^"^^ A^ ^ 

 Shell subconical, higher than wide, consisting of three or four 



volutions, the first of which are small; the last one ventricose 



and angular on the periphery, and concave below, with a distinct 



umbilicus. 



The surface is marked by concentric striae, which are closely 

 arranged and little elevated. On the last volution there is a distinct 

 carina just below the suture, and the periphery is triply carinate, 

 enclosing two depressed bands, upon which the concentric striae 

 are abruptly bent backwards from the aperture. At a distance below 

 the periphery equal to that between the upper carina and the cen- 

 tral one, are one or two carinate revolving lines. 



This species, though observed only in imperfect specimens, is readily 

 distinguished from any others of the group. 



Geological formation and locality. In the shales of the Hamilton group: 

 Seneca lake shore, N.Y. 

 1861.] 



