164 Silurian Fossils of Canada. 



and in perfect specimens the width must be nearly twice the 

 height. There are about four whorls. The surface appears to be 

 nearly smooth, but as the only specimens with the shell preserved, 

 that I have seen are silicified, they do not exhibit it perfectly. 



This species differs from all those described by Hall in the 

 Palseontology of New York in having the umbilicus closed and 

 from the P. lenticularis and P. qualteriatus of the European 

 authors, not only in the same respect, but also in having the mar- 

 gin rounded instead of acute. 



Locality and Formation. — City of Ottawa; near Montreal; 

 Belleville ; Trenton, and numerous other localities in Trenton 

 Limestone ; good specimens extremely rare. 



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



Pleurotomaria Americana. 



P. lenticularis ?— Hall, Pal. N. Y., p. 172. 

 Not P. lenticularis. — Of European Authors. 



Fig. 7. 



Fig. Y. — Phurotoraaria Americana. A section through the umbilicus. 

 General form same as P. Progne, (see fig. 6) from which 

 species it only differs in having an open umbilicus. 



Description. — Lenticular, one or two inches wide ; whorls four 

 or five, nearly fiat above, elevated into a depressed conical spire 

 with a nearly smooth continuous slope from the apex to the mar- 

 gin ; the latter obtusely rounded. On the under side the whorls 

 are moderately convex, forming a depressed conical base, the bulk 

 of which is always somewhat greater than that of the spire. The 

 umbilicus penetrates to the apex, and is in general somewhat less 

 than one third of the whole width of the shell. The aperture is 

 transversely sub-rhomboidal, the width about one third greater 

 than the height. 



The surface is rarely preserved, but from such fragments of the 

 shell as I have seen it must be nearly smooth or at least very 

 finely striated. 



