742 



MR. C. TATE REGAN ON 



[June 19, 



the three rods may be present, but short and not convei-gent 

 anterioi"ly, or they may be enth^ely absent (text-fig. 118, 0). 



Text-fi^. 118. 



Crania of Scymnorliinus (A), Carcliarias (B), and Orectolohus (C), seen from 

 above. (A and B after Gegeubaur, C after Haswell.) 



r, rostrum ; n, nasal capsules. 



The calcification of the vei^tebral centra, although subject to 

 considerable modifications within the group, is nevertheless of 

 great importance in determining the relationships of the families. 

 The primary calcifications take the form of a series of double cones 

 which constrict the notochord vertebrally. In the Odontaspidid?e, 

 Lamnidse, and most Orectolobidfe, the secondary calcifications, 

 usually deposited as concentric laminee, radiate from these to the 

 periphery in such a way as to leave four principal uncalcified areas 

 running from the central double cone to the bases of the neural and 

 hfemal arches (text-fig. 116, A, B & 0, p. 736). In ChiloscyUkim 

 and in the Scyliorhinidfe and Carchariidfe, modifications of this 

 arrangement result from a tendency for these calcifications to start, 

 not from the central double cone, but from points nearer the 

 periphery. In the Carchariidfe and Scyliorhinidse, there may be 

 developed four calcified rays, running from the central double 

 cone into the four principal uncalcified areas above mentioned 

 (text-fig. 116, C). The extreme of specialisation is reached in the 

 Scyliorhinid genera Pristiurus and Pseudotriacis, in which the 

 secondary calcification is represented only by a thin peripheral 

 layer. 



The dorsal and anal fins have their cartilaginous supports 

 typically well-developed, numerous and regularly arranged, with 

 little tendency to fusion (text-fig. 120, A, p. 747). 



The pectoral fin in the Odontaspididfe, Lamnidse, Scyliorhinidse, 

 and CarchariidEB has perhaps a more primitive structure than in 



