I04 FOSSIL CHIAfyE/WIDS 



a Jurassic form (Fig. 105 A), the skeletal structures are 

 readily comparable to those of Fig. 105. In the case of 

 two of the Mesozoic genera, however, the evolution of 

 the Chimaeroids had evidently attained a high degree 

 of specialization : Myriacanthus and Squaloraja, whose par- 

 tial restoration has been attempted in Figs. 106 and 

 106 A, must be both looked upon as highly modified forms ; 

 their snouts and frontal spines are greatly enlarged, and 

 their dental plates (Figs. 107 and 108) widely divergent 

 from the general Chimaeroid type : in Myriacanthus a series 

 of membrane bones occurs in the head region (Fig. 106, 

 B, C). In Squaloraja a horizontally flattened body shape 

 parallels the development of the ray-like form of sharks. 



Fig. 105A. — The Mesozoic Chimaeroid Ischyodus. X \. (After Z[TTEL.) 



Living Chijnceroids 



The Chimaeroids of to-day must be looked upon as the 

 survivors of a group comparatively numerous in Mesozoic 

 times : the few existing forms accordingly, from the palae- 

 ontological standpoint, acquire an exceptional interest. 

 They have been grouped under three genera, — Harriotta, 

 CallorhyncJins, and Chimcera. The first of these (Fig. 

 117, A, B, C) has been only recently discovered, and but 

 a few examples have been taken ; it merits especial atten- 

 tion, since it is unquestionably the most shark-like of 

 known Chimaeroids. In the male it lacks entirely the 

 frontal spine and has its claspers in an exceedingly un- 



