1906.] 



SELACUIAX riSUES. 



733 



Fleicrotremata (con.). 



Cianium without cartilages at- 

 tached to the olfactory ca,p- 

 sules* (text-fig. 118, p. 742). 



Pteiygo-qnadrate with a proce.ss 

 (palato-hasal process of Ge- 

 genbaur) which is ai ticulated 

 or attached hy ligament to 

 the cranium. 



Hyomandibular and cei'atohyal 

 both bearing cartilaginous 

 rays and suppoi-ting the 

 first hemibranch ; ceratohyal 

 a single cartilage attached to 

 the loAver end of the hyo- 

 mandibular (text-fig. 115, 

 p. 734.) 



Ilypotremata (con.). 



Paired prfeorbital cai-tilages, 

 attached or articulated to the 

 olfactory capsules, always 

 present and well-developed 

 (text-fig. 122, p. 753). 



Pterygo-quadrnte without pala- 

 to-basal process, not attached 

 or articulated to the cranium. 



Hyomandibular purely suspen- 

 sory,not bearing cartilaginous 

 rays ; first hemibianch sup- 

 ported ordy by the cei'atohyal, 

 which is segmented into 2 or 

 3 pieces and is either attached 

 high up on the posterior edge 

 of the hyomandibular or else 

 is entii'ely separated from it. 



It would be difficult to imagine a gi-oup more natural or better 

 defined by a number of anatomical peculiarities than the Hypo- 

 ti'emata. The idea sometimes expressed that the ventral position 

 of the gill-clefts is of little impoitance, and that PriHtwplioriiH and 

 Sqimtma would be almost as well placed among the Rays as with 

 the Sharks, is founded on ignorance of tlie many and sticking 

 differeijces between the Sharks and the Rays. 



Dr. Smith Woodward divides the Euselachii iuto two groups, to 

 which he applies Hasse's terms Asterospondyli and Tectospondyli, 

 the latter including the Rays and the Sharks without an anal fin. 

 This is so far natural in that there can be no doubt that the loss 

 of the anal fin in the Sqiialidai! indicates affinity to the Hypotre- 

 mata, Init it does not take into account the resemblances between 

 the Cestraciontidee and the Squalidfe or the differences between 

 the latter and the Hypotremata. 



Dr. Woodward has been influenced by the resemblance of 

 Pristiophorus to Pristis and by the Ray-like features of Hquaiina. 

 The Tectospondyli are also said to be characterised by the presence 

 of large spiracles, even in the most specialised forms ; but this 

 does not hold good for pelagic Sharks of this group (e. g. Homniosus), 

 a^nd Ground-Sharks of the other (e. g. Orectolohiis) ha\ e the spiracles 

 as large as in the Rays. A supposed difference in the sti-ucture 

 of the vertebral column is the remaining reason for the recogni- 

 tion of the Asterospondyli and Tectospondyli, the latter being 

 defined as having the vertebrae, v/hen fully developjed, with the 

 concentric calcified laminae predominating over the radiating 

 laminae, and the foi-mer as having the radiating laminae predo- 



* Paii'ed processes of the prjeorbital mar^'n of the ethmoidal region may be present, 

 and ill Septranchias segment off as separate cartilages. 



