134 
PALAEONTOLOGY OF NEW YORK. 
by strife of growth which are crowded into fascicles, and often become strong 
ridges near the suture-line and on the lower part of the outer volution. The 
prominent portion of the volution, about one-third below the suture, is irregu¬ 
larly and obscurely marked by a series of undefined oblique nodes. The carina 
above the suture-line is a conspicuous feature in well-preserved specimens 
(the one figured has been exfoliated in the upper part), and is continued on the 
outer volution as represented in the figure. 
This fossil, originally described as a Pleurotomaria, has the general form of 
Pleurotomaria subcpnica, Hall, of the Lower Silurian ro'cks; but a critical 
examination shows that it does not possess the peripheral band which is 
characteristic of that genus. The apparent band is simply a projecting ridge, 
over which the strim are curved in the same manner as over other inequalities 
of the surface on the upper part of the last volution. The surface strife, 
moreover, are of different character, being striae of growth crowded into 
fascicles, and producing an unevenly ridged surface. Having no cancellating 
revolving strife, it wants, in this respect, a common element in the surface 
of Pleurotomaria. The aperture is transversely suboval, and there is no 
columella extending below, nor an open umbilicus. The aperture, form and 
general aspect of the shell indicate its relations with the Trochidfe; and I 
see no good reasons why it may not be embraced in the Linnean genus Trochus. 
I have therefore proposed for it the above subgeneric name. 
Formation and locality. In limestone of the age of the Upper Helderberg 
group, near Sandusky, Ohio. 
. The casts of this species bear considerable resemblance to Pleurotomaria 
Griffithii, of McCoy, which is described as “acutely conical; whorls flat; a 
single, very prominent square keel in the middle of the body-whorl, but 
continued along the base of the spiral whorls close to the suture.” The 
surface-markings are not described or represented in the figure, which is from 
a cast of the interior. The general form of the fossil, the strong peripheral 
keel and other features, render it very probable that it is generically identical 
with the P. Kearneyi, while some of its characters seem incompatible with 
Pleurotomaria. 
