ORDER ELASMOBRANCHEI. 



945 



the crowns of the teeth (fig. 872), which are generally devoid of 

 basal cusps. It has been recorded from the Jurassic, and occurs 

 abundantly in the Chalk of Europe, India, and New Zealand, and 

 is also represented in the European Miocene. Teeth from the 

 Upper Cretaceous of Europe and India, differing from those of 

 Lamna by the nearly circular section of their crowns, have been 

 referred to the existing genus Odontaspis ; but Mr S. Woodward 

 considers that they belong to a genus from the Cretaceous of the 

 Lebanon, originally described under the preoccupied name of Rhino- 

 gtiathus, but now known as Scapanorhynchus. Odontaspis itself 

 occurs in the Eocene. Teeth of a long and slender type, from the 

 Upper Jurassic and Lower Cretaceous, have been described under 



Fig. 873. — Tooth of Carcharodon megalodon, from the Miocene of Malta. (After Zittel.) 



the name of Sphe?wdus, now changed to Orthacodus. Other teeth, 

 from the Continental Miocene, have been referred to the existing 

 genus Alopecias or "Threshers." With Carcharodon we come to 

 Sharks of enormous size, characterised by their large, flat, and reg- 

 ularly triangular teeth (fig. 873), in which the edges are serrated, 

 and there are no basal cusps. The one existing species attains a 

 length of 40 feet, and has teeth measuring a little over 2 inches 

 along the margins, with a basal width of 1.8 inches. It occurs fossil 

 in the Pliocene of Europe. In the Red Crag, and also at the bottom 

 of the Pacific, teeth are, however, found in which the corresponding 

 dimensions are 5 and 4 inches, and thus indicate enormous indi- 



