172 Silurian Fossils of Canada. 



cimen, the position of this siphuncle would be close to the ventral 

 side of the shell. Another siphuncle about the same size shows 

 seven septal rings to the inch. In a third, consisting of a portion 

 of the larger extremity of an individual which, when perfect, must 

 have been at least nine inches in length, there are six septa partly 

 preserved apparently those next the aperture. They are dis- 

 tant from each other about five lines, the whole being com- 

 prised within a length of thirty lines. The shell where these 

 septa are situated is at least four inches in diameter in the 

 transverse direction, and the siphuncle about two inches. The 

 edges of the septa, in crossing the ventral or concave side, make 

 at the surface a short curve towards the apex, but on the siphun- 

 cle the septal ridges cross from the dorsal to the ventral side ob- 

 liquely, so that on the ventral side they are somewhat nearer the 

 aperture than they are on the dorsal side. 



The above are all the details of this species of any importance 

 furnished by our specimens. On comparison with Salter's P. in- 

 vaginatum, it will be seen that the septal rings do not cross the 

 siphuncle in the same direction as they do in ours, and further, 

 that that species is more broadly curved. 



Locality and Formation. — Mingan Islands, Calciferous Sand- 

 rock. 



Collectors. — Sir W. E. Logan. J. Richardson. 



Cyrtoceras exiguum. N. s. 



Fig IT. Fig. 18. 



Fig. It. — Cyrtoceras exiguum. Outline of a specimen. The dotted 

 lines represents the supposed outline of the smaller extre- 

 mity. 

 18. — A specimen shewing the depth of the chamber of habitation 

 and five of the air chambers. 



Description. — Small, slender, slightly curved ; section circular. 

 One of the specimens examined is three lines in diameter at the 

 aperture and apparently a little less at one line and a half above. 

 The shell then expands to a diameter of four lines at the distance 

 of five lines from the aperture. It then tapers to two lines at a 



