S QUA TINA AND PRISTIS 



91 



The different families of the existing sharks appear to 

 to have been already differentiated during the early Meso- 

 zoic times. The ancient shark-like form had then given 

 place to the flattened and rostrated types, adapted to the 



Fig. 96 B. — The Greenland shark, Lcemargus borealis, L. X 3V. (After GiJNTHER.) 



conditions of bottom living and to the special character of 

 their shell-fish or crustacean diet. 



One of the earliest offshoots from the main selachian 

 stem appears to have been Sqttatina (Fig. 97), popularly 

 known as the monk-fish, or angel-fish. As early as the 

 Mesozoic times it was existing, differing but little from the 

 recent species. Its general shape is shark-like, although its 



Fig. 97. — The monk-, or angel-fish, Rhlna squatina. 5. X iV. Atlantic, 

 Mediterranean, Pacific. 



head and trunk are clearly depressed. This, together with 

 its enlarged pectoral fins, enables it to take a position 

 closer to the bottom. 



The recent saw-fish, Pristis (Figs. 98, 98 A\ is next to 



