104 FOSSIL CHIMAEROIDS 
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 Chimezeroids had evidently attained a high degree 
of specialization: Myriacanthus and Sgualoraja, 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 Chimzeroid 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. 105 A. — The Mesozoic Chimeeroid /schyodus. Xx 4. (After ZITTEL.) 
Living Chimeroids 
The Chimzeroids 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 palz- 
ontological standpoint, acquire an exceptional interest. 
They have been grouped under three genera, — Harriotta, 
Callorhynchus, and Chimera. 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 Chimezeroids. In the male it lacks entirely the 
frontal spine and has its claspers in an exceedingly un- 
