VEETEBEATA 



21 



Fig. 4, — Tails of fishes; A^ diphycercal tail of Polypterus; B, dlphyheterocercal tail of Cocco- 

 steus; C, caudal fin of a shark (Centrina); Z), end of vertebral column of trout {Salmo fario); 

 E, end of vertebral column of barbel (Barbus fluviatilis) ; ep, Epural; hy, hypural bones. 



Subclass I.— ELASMOBRANCHII. 



The sharks are divided into three orders, as follows: 

 Paired fins ptychopterygial ; with axonosts 



