•164 Fossils of the Chazy Limestone. 



Locality and Formation* — Chazy limestone, Mingan Islands. 

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



Besides the above, there are three other species of Orthoceras in 

 Chazy limestone, of which one resembles 0. Ottawaense, and may 

 yet turn out to be the same. 



Genus Nautilus. 



In the genus Trocholites (Conrad) the siphuncle is internal, in 

 Nautilus central, and in Cryptoceras (d'Orbigny) external. There 

 are many palaeontologists who think that the first and last of these 

 should be retained as genera or sub-genera distinct from Nautilusi 

 while others are of opinion that all should be comprised under one 

 name. The position of the siphuncle can hardly be regarded as 

 of generic importance. In Cyrtoceras and Phragmoceras it is 

 dorsal, central, or ventral. If we should divide Nautilus into 

 three genera, according to the position of the siphuncle, then 

 Cyrtoceras and Phragmoceras must also be subdivided in order to 

 make our genera of equa/ value. We would thus have nine 

 genera where there are only three. Professor Chapman of Toronto 

 was the first to direct attention to the fact that Lituites undatus 

 (Hall), and another species which occurs at Lorette and which I 

 had considered to be identical with Hall's species, do not belong 

 to Lituites, but rather *,o d'Orbigny's genus Cryptoceras* . This 

 view is confirmed by several other specimens collected since Prof. 

 Chapman's article was written ; and should Cryptoceras be retain- 

 ed, at least two of the following species must be referred to it, 

 since both have an external siphuncle. In the other, (Nautilus 

 natator), it has not been observed. I have examined all our 

 specimens carefully in order to ascertain the direction of the 

 bent portion of the septa around the siphuncle, but, owing to 

 their imperfection, without success. Should it be found hereafter 

 to be directed forward, then the species must be transferred to 

 Barrande's new genus, Nothoceras. 



Nautilus Jason, N. s. 



Description. — Discoid, planorbiform, all the whorls exposed in 

 the umbilicus. Section of shell broad oval, the ventral and dor- 



* On the occurrence of the genus Cryptoceras in Silurian Rocks. By 

 E.J. Chapman, Professor of Mineralogy and Geology in University Col- 

 lege, Toronto. Canadian Journal, 2nd series, vol. 2, page 264 ; and in 

 Annals of Natural History, 2nd series, vol. 2, page 114. 



