92 SA W-FISHES 
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. @%. X as. 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 Pristiophorus 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 
