96 KINSHIPS OF SHARKS 
Affinities 
In concluding the present chapter, the probable affini- 
ties and interrelationships of the Elasmobranchs may be 
summarized as follows (v. Fig. 103) :— 
1. Of all known stems that of the shark is most: nearly 
ancestral in the line of jaw-bearing vertebrates. 
2. A generalized form not unlike Cladoselache might 
well represent the ancestor of Pleuracanthid, as well as , 
of the primitive Cestraciont, of Acanthodes, and of the 
modern sharks and rays. 
Fig. 102 A. — The mantis, or devil ray, Cephaloptera (Dicerobatis) draco. X te. — 
(After GUNTHER.) Tropical seas. 
3. On the evidence of the Permian Pleuracanthids, 
lung-fishes (Dipnoans) and the earliest bony fishes 
(Crossopterygians) are to be derived from an advancing — 
shark type. ‘ 
4. From the ancestral stem of the recent sharks 
Cestracionts were the most early differentiated: it is one 
of their more generalized forms, Cestracion, that has alone 
