Silurian Fossils of Canada, 176 



rowly rounded. Siplmncle very small, close to the ventral margin 

 sliglitly dilated between the septa ; of these latter there are six in 

 three lines where the transverse diameter of the shell is five lines. 



The dimensions of the best preserved specimen that I have seen 

 are as follows. Length of specimen twenty-two lines ; transverse 

 diameter of aperture seven lines ; dorso-ventral diameter of aper- 

 ture five lines ; depth of chamber of habitation, twelve lines ; 

 transverse diameter at smaller extremity of specimen four lines 

 nearly ; dorso-ventral diameter three lines nearly. In the length 

 of twenty-two lines measuring from the aperture this specimen 

 tapers three lines in the tranverse diameter and one line in the 

 dorso-ventral diameters. The width of the siphuncle between the 

 septa is about three-fourths of a line ; its passage through the 

 septa is a small circular aperture scarcely one third of a line in 

 diameter. At the smaller end of this specimen the greatest trans- 

 verse width is about one fourth the dorso-ventral diameter from 

 the ventral margin. The aperture is more nearly a regular oval. 

 The siphuncle is in the middle of the ventral aspect. The shell 

 is gently curved towards the dorsal side. 



This species is related to both 0. xijjMas and 0. Jiastatum, 

 (Report for 1856, p. 318 and 333) but the proportions are very 

 difierent. In 0. xipkias the two diameters of the aperture are 

 to each other as 7 to 3, but in 0. tener they are as 7 to 5. 0. 

 hastatum tapers at the rate of about 4 lines to the inch, while in 

 0. tener the rate is scarcely two lines. 



Locality and Formation. — Black River limestone. Pauquettes 

 Rapids. 



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



Orthoceras pertinax. N. s. 



Description. — The specimen on which this species is founded 

 is two inches and five lines in length ; nine lines in diameter at 

 the larger and seven lines at the smaller extremity ; section cir- 

 cular ; septa distant three lines at the large end and two lines and 

 a-half at the small end. The siphuncle is moniliform its centre 

 distant two lines from the marsrin where the diameter is seven 

 lines ; the expansions are sub-globular and about two lines or a 

 little more in their greatest diameter. The septa have a convex- 

 ity equal to about half their distance from each other and they 

 cross the tube obliquely so that their edges at the surface on the 



