174 



twelve to twenty in an inch. These stiije cross the shell obliquely, cur- 

 Ting towards the apex on the ventral side. Chamber of habitation 

 unknown. 



Judging from the fragments that^have been collected, this orthoceratite 

 must attain a length of four or five feet. The following are the dimensions 

 of several specimens : 



1. Length 13 inches ; diameter of shell at the longer extremity 32 

 lines, and of the siphuncle 10 lines ; diameter of shell at smaller ex- 

 tremity 15 lines, and of the siphuncle 5 lines. 



2. Length 10 inches ; diameter of shell at the larger extremity 26 

 lines, siphuncle 8 lines ; diameter of shell at smaller extremity 16 hues, 

 siphuncle 5| lines. 



3. Length 6 inches ; diameter of shell 22 and 15 lines ; siphuncle 

 7^ and 5 lines. 



The siphuncle is sometimes found separate, and is always strongly 

 marked by obhque encircling lines, indicating the positions of the junction 

 of the septa with it. The smaller extremity is also filled with the organic 

 deposit so characteristic of species of this type. 



This species must be closely allied to 0. rapax, but has a more slender 

 siphuncle. 



Locality and Formation. — Mingan Islands, Islands of Montreal and 

 Bizard, in loose blocks near Cornwall ; Chazy limestone. 



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



Orthoceras diffidens. (N. sp.) 



Description. — Apparently about one foot in length ; section circular ; 

 tapering at the rate of from one and a half to two lines to the inch ; septa 

 from four to five to the inch, rather strongly concave. The siphuncle is 

 monihform, the segments between the septa subglobular or ovate, the diame- 

 ter of each being equal to about one-fifth the whole diameter of the shell. 

 The position of the siphuncle, as shown in three different individuals, is, 

 with its centre, about half way between the centre of the shell and the 

 margin ; it is a little more distant from the margin than it is from the 

 centre of the fossil. 



This species, both internally and externally, closely resembles 0, 

 AUumettense, so common in the Black River Umestone. The siphuncle 

 of that species, however, is in general larger, being usually onc-thuxl the 

 whole width, rarely one-fourth. 



Length, from 8 to 12 inches ; diameter at aperture, 1 to 1| inches. 



Locality and Formation. — Mingan Islands ; Chazy. 



Collector. — J. Richardson. 



