92 



SA W-FISIIKS 



be mentioned as a form somewhat transitional from shark 

 to ray. Its body, as may be seen in the figure, has been 

 strikingly flattened, the gill openings changing their posi- 

 tion from the lateral to the ventral side, but the fins re- 

 taining in general the selachian characters. Its singular 

 rostrum with lateral spike-like teeth is unquestionably a 



Fig. 98. — The saw-fish. Pristis pectinatus, Latham. 5. X jo. Tropical 

 seas. (After Goode in U. S. F. C.) 



highly specialized organ. Pristis is thus far known not 

 earlier than the Eocene, but its close connection genetically 

 with the ancient and more generalized PristiopJiojnis is 

 usually conceded. 



Pristiophorus (Fig. 99) is certainly more closely allied 

 to the sharks : its gill slits have not as yet acquired their 

 ventral position, and its rostrum suggests the ancestral 



Fig. 98 A. — Saw-fish, ventral view. 



conditions of that of Pristis. Its barbel-like structures, 

 however, distinguish this form clearly from all other 

 Elasmobranchs. It is known to have occurred as early 

 as the Jura. 



The Skates or Rays are well known to represent the 

 most highly modified survivors of the ancient stem of the 



