462 Fossils of the Chazy Limestone. 



yet positively established. The longitudinal striae are continuous 

 over the edges of the annulations. The segments of the siphuncle 

 are moderately inflated between the septa. 



Where the diameter is one inch the depth of the concavity of 

 the septa is equal to the distance between them, or a little less, 

 but towards the smaller extremity the septa are not so strongly 

 concave. 



The amount of the curvature of the shell appears to be a little 

 variable, but the average in the three specimens I have examined 

 would be equal to that of an arch with a base of eight inches and 

 an elevation of three lines in the middle. 



This species seems to be allied to 0. annellum (Conrad), but 

 the figures given in the "Palaeontology of New York," volume 1, 

 plate 43, shew that the spaces between the annulations in that 

 species are not concave. Figure 6a on the plate cited has sharp- 

 edged annulations with angular constrictions between. Fig. 6d 

 shews broadly-rounded annulation?, with sharp angular constric- 

 tions. If these figures be correct they represent two very differ- 

 ent species, and neither of them identical with the one above 

 described. Neither Hall nor Conrad state whether the inter- 

 annular spaces in 0. annellum are concave or not. 



Locality and Formation. — Mingan Islands; Chazy limestone. 



Collectors. — Sir "W. E. Losfan, J. Richardson. 



Orthoceras multicameratum (Conrad). 



This species occurs at the Mingan Islands, and also on the 

 Island of Montreal in the Chazy limestone; also in the Black River 

 limestone in the township of Westmeath. 



Orthoceras bilineatum (Hall). 



Occurs in the Chazy at Mingan ; in the Black River limestone 

 at La Petite Chaudiere near Ottawa, and at Pauquette's Rapids. 

 In the Hudson River group at Cape Smith, Lake Huron. 



Orthoceras subarcuatum (Hall). 



This species has been found in the Chazy on the island of 

 Montreal and near Cornwall. The surface characters are not well 

 known, but one of the specimens exhibits the siphuncle, which is 

 strongly moniliform, and situated half way between the centre 

 and the outside. All the specimens that I have seen are curved. 



