THE 



CANADIAN NATURALIST 



AND 



^uailctly ^ouvnat ol ^dciKC* 



PAL^ONTOLOGICAL NOTES. 



By J. W. Dawson, LL.D., F.R.S. 



I. A New Species of Piloceras. 



(Figs. 1, 2.) 



This genus was established by Salter, in 1858,* for a very 

 curious shell found in Scotland, in the Durness Limestone, one 

 of the lowest members of the Lower Silurian or possibly within 

 the limits of the Upper Cumbrian. Salter found in this limestone 

 two species of the genus, but one was too imperfect for descrip- 

 tivjn. The typical species P. invaginatum he regarded as the 

 shell of a cephalopod mollusk allied to Orthoceras, but of very 

 simple structure, having the chamber and siphuncle united into 

 one organ. His definition of the genus was in these words : 

 " siphuncle and septa combined, as a series of conical concave 

 septa which fit into each other sheathwise." 



In 1860, Billings described, in the Canadian Naturalist, j a 

 species from the Calciferous Formation of Belleisle, under the 

 name Piloceras Canadense. The specimens showed that the part 

 described by Salter was not the external shell, but only the 

 siphuncle, and that the shell, when complete, must have included 

 a chambered portion surrounding this enormous siphuncle, which 

 thus corresponde(^^o the great siphuncle of the Lower Silurian 

 shells known as yndoceras. Having thus ascertained the exist- 



* Journal of Geological Society of London, Vol. XV. 

 t Vol. V. 



Vol. X. A No. 1. 



