Silurian Fossils of Canada. 163 



wliich on crossing the wliorl are deflected gently backwards until 

 on approaching the base of the body whorl, they turn a little for- 

 ward and pass vertically into the umbilicus. There are six strias 

 in the width of one line. Width of only specimen seen five lines, 

 height four lines ; width of aperture two and a half lines. 



This species differs from S. Circe in being much smaller, and in 

 having the surface so strongly striated as to present a pecu- 

 liarly rough file-like appearance ; only one specimen has been col- 

 lected, but as it exhibits the aspect of a mature shell, I am in- 

 clined to think the species is small. 



Locality and Formation. — Pauquettes Rapids, Ottawa River, 

 Black River, and Birdseye, (apparently rare). 



Collector. — Sir W. E. Logan. 



The following species of Pleurotomaria have been usually 

 referred to P. lenficularis, (Sowerby) but they all appear to be 

 distinct from that species. 



Pleurotomaria Progne. N. s. 



Fig. 6. 

 Fig. 6. — Pleurotomaria Progne. 



Decription. — Lenticular ; about one inch and a half in width ; 

 spire depressed conical, apical angle about 140°, seldom more but 

 often a little less ; surface of spire presenting an uniform nearly 

 flat, smooth slope from the apex to the margin, the sutures in 

 perfect specimens being scarcely distinguishable although in casts 

 of the interior they are somewhat strong and deep. The margin 

 is narrowly rounded and does not exhibit the acute edge possessed 

 by such species as P. qualteriatus. On the under side the whorls 

 are uniformly depressed convex and the base, or all that portion 

 of the shell which lies below the margin, is usually nearly double 

 the bulk of the spire. When perfect the umbilicus is completely 

 closed, but in the casts of the interior, there is a small perforation. 

 The aperture is transversely sub-oval, scarcely sub-rhomboidal 



