184 THE CANADIAN NATURALIST. June 



NOTES ON SOME OF THE MORE REMARKABLE 

 GENERA OF SILURIAN AND DEVONIAN FOSSILS, 



By E. Billings, F.G.S. 



Genus Receptaculites, Defrance. 



1. — Diagram of the structure of Receptaculites as it would be shown 

 in a vertical section through a sub-conical species, a, the aperture 

 in the summit ; b, the endorhin or inner integument lining the central 

 cavity ; c, the ectorhin or external integument ; n, the usual posi- 

 tion of the nucleus ; v, the great internal cavity. The unshaded bands 

 running from the ectorhin to the endorhin represent the tubes. 



The structure and zoological position of Receptaculites have 

 been more or less elaborately investigated by Goldfuss, Eichwald, 

 Roemer, Salter, Hall, and other eminent observers, and yet, owing 

 to the imperfection of the materials, a great deal remains to be 

 done before the various questions involved in the relations of this 

 curious genus can be regarded as positively settled. Since the 

 publication of Salter's paper in the first Decade of our Geological 

 Survey, numerous specimens of several distinct species have been 

 collected in the Silurian rocks of Canada, and I am, by the study 

 of these, now enabled to furnish a few additional details. The 

 principal new points are, the perforated structure of the internal 

 integument, the existence (in most, if not in all, of the species) of 

 a great central cavity and an orifice in the upper side. The flat 

 watch-shaped specimens which are usually figured as constituting 

 the whole of the body, are probably only the basal portion of the 

 body-wall of the discoid species. 



