24 



grooves, one of which forms the anterior boundary of the keel which 

 encircles the periphery. 



Maximum height of the most perfect specimen collected, twenty- 

 one millimetres: breadth of the same, twenty-five mm. 



Durham, Mr. J. Townsend : two specimens, both with the test pre- 

 served. 



One of the most curious featui-es of this species is the extreme thick- 

 ening of the shell on the periphery of the last volution, from which 

 it results that although the outer lip is shai-ply carinated exteriorly, 

 yet the mouth or aperture is almost exactly circular in outline. This 

 peculiar character is seen also in the Pterocheilos primus of Moore, 

 from the English Lias, but in that genus the columella is much produced 

 anteriorly, which is by no means the case with the present species. 



P. cyclostoma appears to differ fi-om P. hispiralis of Hall, from the 

 Guelph formation, principally in its more obliquely flattened and less 

 ventricose spire, its indistinct suture and its much naiTOwer spiral 

 band. 



Pleurotomaria Durhamensis. (N. Sp.) 

 Plate 4, fig. 2. 



Shell turbinate-conical, a little higher than broad ; spire moderately 

 elevated, about equal to the body-whorl in height, its upper portion 

 distinctly acuminated; whorls eight or nine, the first five or six 

 increasing very slowly in size and obliquely compressed but not angu- 

 lated, the next two, which immediately precede the body- whorl, 

 increasing much more rapidly both in height and breadth and rather 

 strongly angulated below the middle : body-whorl angulated a little 

 above the middle and obli-quely flattened above the angle ; base convex 

 and evenly rounded; umbilicus about one third the diameter of the 

 base and apparently deep. Sui-face markings unknown. 



Height, twenty-six millimetres : breadth, twenty mm. 



Durham, Mr. J. Townsend : a single but very perfect cast. 



The general outline of this shell is not at all unlike that of the 

 Straparollina pelagica of Billings, from the Quebec Group of Newfound- 

 land, but in the latter species the whorls are said to be only five or six 

 in number and the lower ones are not distinctly angulated. 



M0RCHISONIA Hespelerensis. (N. Sp.) 

 Plate 4, fig. 3. 



Shell angularly turbinated, not much elongated, the lengtli beino' 

 about one third gi-eater than the breadth : spire about equal to the 



