The Class Elasmobranchii or Shark-like Fishes 5 i 5 



fins consist each of a single stout spine, nearly or quite destitute 

 of other rays. A similar spine is placed in front of the dorsal 



Fig. .301. — Cladoselache pjUri (Newberry), restored. Ventral view. (After Dean.) 



fin and one in front of the anal. According to Dean these 

 spines are each produced by the growing together of all the 



Fig. 302. — Teeth of Cladoselache fyleri (Newberry). (After Dean.) 



fin-rays normally belonging to the fin, a view of their mor- 

 phology not universally accepted. 



The dermal covering is highly specialized, the shagreen den- 



FlG. 303. — Acanthoessus loardi (ERorton). Carboniferous. Family Acanlhoessida:. 



(After Woodward.) 



tides being much enlarged and thickened, often set in lit- 

 tle squares suggesting a checker-board. The skull is covered 

 with small bony plates and membrane bones form a sort of 

 ring about the eye. The teeth are few, large, and "degenerate 



