Silurian Fossils of Canada, 165 



This is the most common species of Pleurotomaria in the 

 Trenton Limestone, and is I have no doubt the same as that 

 figured by Prof. Hall in the work above cited, but surely it can- 

 not be the European species P. lenticularis to which it has been 

 referred. That species has a sharp edged margin. There are several 

 European species under the name P. lenticularis^ but it is the 

 Silurian form to which I refer. 



P. rotuloides. — (Hall) has not the smooth spire, and concealed 

 suture of P. Americana^ and there is no other in the Palaeonto- 

 logy of New York, to which this species can be compared. It 

 may be that P. Progne and P. Americana should be classified as 

 one species, but at present I think the great difference in the um- 

 bilicus is sufficient to separate them. 



Locality and Formation. — Trenton Limestone at Ottawa, 

 Montreal, Beauport, Trenton, Belleville, and St. Joseph's Island, 

 Lake Huron. Good specimens exceedingly rare. 



Collectors,— ^ir W. E. L.; A.M.; J. R.; E. B.; R. B. 



Pleurotomaria Helena. N. s. 



Fig. 8. 

 Fig. 8. — Pleurotomaria Helena. 



Description. — Sub-lenticular, with an elevated narrowly round- 

 ed margin ; spire depressed conical ; apical angle varying from 110° 

 to 125°, apex rounded not acute ; whorls about four, the last one 

 rather strongly concave on the upper side, the others only slightly 

 so. On the underside of the shell the whorls are moderately con- 

 vex, and the umbilicus closed. The aperture is a little wider than 

 high, the upper part of the inner lip slightly indented by the 

 body whorl, the lower half somewhat vertical, but rounded, the 

 lower part of the outer lip from the umbilicus to the margin of 

 the whorl gently convex, the portion above the margin concave. 

 In most specimens the suture is enamelled, the shell appearing to 

 be continuous from the apex to the margin, but in some, especially 



