Further Notes on Carhoniferous Selachii. 421 



never show more than two cones, a large one and one small 

 lateral one, which is absent in some specimens, ought to be 

 included in a new genus distinct from Gladodus. I therefore 

 propose for this form the name Dicentrochos, and venture to 

 express an opinion that it will turn out to be more allied to 

 Diplodus than to Gladodus. 



XXXV. Further Notes on Carhoniferous Selachii. By Dr 

 E. H. Tkaqltair, F.E.S, F.G.S. 



(Bead 15tli February 1888. Appeared also in the Geological Magazine for 

 March 1888.) 



Anodontacanthus and Pleur acanthus. 



In 18811 Mr j_ ^_ Davis proposed the genus Anodonta- 

 canthus for certain straight spines resembling Pleur acanthus, 

 but differing in the absence of the two rows of denticles. 

 Three species are included : — A. acutus and oUusus, from the 

 Coal-measures of Yorkshire, and A. fastigiatiis, from the 

 Blackband Ironstone of Carboniferous Limestone age at 

 Loanhead, near Edinburgh. 



I offer no criticisms on the two Yorkshire species, nor have 

 I seen the type of the Midlothian A. fastigiatus. In the 

 large collection of spines which I have from Loanhead, there 

 are, however, many which I refer without doubt to the last- 

 named species. Now, although some of these are smooth 

 and without denticles, others show in all stages of apparent 

 wearing away undoubted stumps of denticles, whereby the 

 species fastigiatus falls into Pleur acanthus, as it at present 

 stands. 



It is to be noted that a large number of the spines found 

 in this Ironstone (Loanhead and Borough Lee, ISTo. 2) are 

 singularly worn or eroded all over, as if they had been long 

 exposed to the action of agencies, chemical or mechanical, 

 tending to destroy the surface. I have seen a spine of Gyra- 

 canthus from that bed having every vestio-e of the surface 

 ornament, so elaborate in that genus, removed, and I had to 

 examine it microscopically before I felt absolutely sure of its 



^ Quart. Journ. Geol. Sac, vol. xxvii., p. 427. 



