134 2 ' A L&ONTOL OGY OF NEW Y ORK. 



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- 

 larlv 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 Pleurotomakia, has the general form of 

 Pleurotomaria subconica, Hall, of the Lower Silurian rocks ; 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 strife are curved in the same manner as over other inequalities 

 of the surface on the upper part of the last volution. The surface striae, 

 moreover, are of different character, being strife 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 Trochidae ; 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. 



