28 CANADIAN FOSSILS. 



on the middle of the whorl are strong, prominent angles, enclosing 

 a broad, vertical, slightly concave space (the upper angle rather the 

 more prom'nent); one close to the deeply canaliculated suture; the 

 fourth only visible on the base, margining a very broad umbilicus. 



The space between the upper and second carina is more concave 

 than that below the latter, while between the third and fourth the 

 space is a little convex, not quite flat. The umbilicus is first concave 

 and then tumid ; it exposes the second and part of the third whorl. 

 The mouth is round-ovate — the obliquity from above outwards — 

 and thickened at the basal angle formed by the lowest keel. 



Hall's specimens are all more or less distorted and compressed ; 

 hence his description, though accurate, does not fully agree in all 

 points. The character of the angular volutions, with the concave 

 spaces between short depressed spire and wide umbilicus, enables us 

 to recognize the species ; and I am further assured by Mr. E. Billings 

 that there is no doubt of their identity. But the species must be 

 more variable than the Canadian specimens shew, since Hall figures 

 and describes forms (plate 3S, figure lg) more elevated, and others 

 (plate 3S, figure le, and plate 10, figure 9 b) more depressed than any 

 of ours. The base of none of his specimens isventricose, and I think 

 that must be due to oblique pressure in his specimens or to their 

 being mostly internal casts. 



The description, by Prof. McCoy, of his Turbo trochlcatus* agrees 

 well with ours, except in the rounded base and small umbilicus ; it 

 has a less deep suture, as his figure shews, and the space between 

 the two bands on the whorl is decidedly narrower. These differences 

 are here noted particularly, as I had provisionally referred the 

 Canadian shell (see Reports British Association, preface) to the T. 

 trochleatus, McCoy. Now that we know the position of the Galway 

 rocks as Middle Silurian, it is the less likely that any species should 

 be in common with those of the lowest formations of Canada. 



Pleurotomaria latifusciata, of the same author, is another species so 

 like ours, that it seems hardly distinguishable, except by the longer 

 spire. 



Locality. — T. umbilicata is a common species occurring in nearly 

 all the slabs from Pauquette's Kapids. It ranges from the Birdseye 

 to the Trenton limestones, in New York. 



• Silurian Fossils, Ireland, plate i., figure 9. 



