SELACHII. 



49 



Cretaceous of Mount Lebanon show that at least some of these 

 teeth belong to extinct genera. Scapanorhynchus, from the 

 Lebanon, has teeth like Odontaspis, but differs from this genus 

 in having a much-elongated rostrum and exhibiting a re- 

 markably extended anal fin. No undoubted Carchariidae occur 

 below the Eocene, where extinct genera are recognized. Their 

 teeth can be distinguished from those of the Lamnidae by the 

 presence of an internal cavity in the former. 



A. 



FIG. 38. 



Oxyrhina crassa ; tooth, external (A) and lateral (B) aspects, nat. size. Pliocene 

 (Bed Crag) ; Suffolk. 



Sub-Order 2. Tectospondyli. 



The typical members of this sub-order are the existing 

 skates, rays, and devil-fishes. Specialization results in a re- 

 markable depression of the body and the enlargement of the 

 pectoral fins, which often meet in advance of the head ; the 

 spiracles are always large. The anal fin is invariably wanting. 

 The vertebral centra, when fully developed, are strengthened 

 by concentric calcified laminae which (with rare and partial 

 exceptions) predominate over the radiating laminae. As among 

 the Asterospondyli, it is difficult to recognize the least-special- 

 ized forms in which the notochord is persistent or the vertebrae 

 w. * 



