348 



a-lialf from each other in specimens from six to twelve lines in diameter. 

 The spaces between the annulations are uniformly concave. All the 

 specimens yet discovered are silicified, but with the surface characters of 

 the shell not preserved. Several have been collected which are slightly- 

 curved. 



The septa increase rapidly in number towards the smaller extremity of 

 the shell, and it would appear also that, in some individuals, the distance 

 between them varies in different parts. In one specimen, where the 

 diameter is five lines, there are five septa in half an inch; but in the next 

 half inch there are eight. The position of the siphuncle is also slightly 

 variable. 



There are several American 'orthoceratites which in fragments, not 

 shewing the internal characters, could hardly be distinguished froni this. 

 0. decrescens of the Trenton tapers somewhat more rapidly, and has a 

 small slightly moniliform siphuncle. 0. Priamus (ante p. 253) has also 

 a smaller siphuncle and tapers more rapidly. 



Locality and Formation. — Mingan Islands, Tow^nship of Godmanchester, 

 Counties of Leeds and Grenville, and Newfoundland. The specimens from 

 the latter locality are doubtfully referred to this species (ante, p. 255). 

 Calciferous formation. 



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



Orthoceras furtivum. (N. sp.) 



Fig. 33Y. 

 Fig. 337. — Orthoceras furtivwn. a, the siphuncle. 



Bescrii^tion. — Obliquely annulated, tapering at the rate of a little less 

 than one line to the inch ; section circular ; siphuncle cylindrical, about 

 one-third 'i the whole diameter, in contact with the shell or nearly so. 

 Septa and surface unknown. 



The annulations are prominent, narrowly rounded, six or seven in the 

 k'ugth of one inch, and slightly obrKjue ; the intervening spaces uniformly 

 concave. The sii)huncle is obscurely seen in the specimen, but of its posi- 



