1906.] 



SELACHIAN FISHES, 



739 



Notidanoidei and Squaloidei (except Sqimtina), the second to the 

 Galeoidei, the third to the Hypotremata and Squatina. The last- 

 named is admitted, however, to belong as much to the Squaloidei 

 as to the Hypotremata. The Holocephali have mixopterygia 

 which differ considerably from the Euselachian type. 



Text-fig. 117. 



€1- ■ - 



td-^' 



Dorsal views of the skeleton of the mixopterygia of Somniosus (A), Lamna (B), and 

 BJiinobatus (C). (All after Jungersen.) In C the covering piece has been 

 removed, and is shown in a ventral view of the terminal part. 



I, pelvic basipterygium ; r, radials; a, accessory cartilage ; p, proximal segments 

 of axial cartilage ; ax, axial cartilage proper ; g, terminal portion of axial 

 cartilage; rd, dorsal marginal cartilage; rv, ventral marginal cartilage; 

 td, dorsal terminal pife<'e ; tv, ventral terminal piece ; t and td.2, terminal pieces ; 

 c, covering piece. 



The Euselachii are the only group which call for a detailed 

 systematic account. 



Order EUSELACHII. 



Suborder 1. PLEUROTREMATA. 



Division 1. Notidanoidei. 



Six or seven gill-clefts on each side ; a single dorsal fin, not 

 preceded by a spine, opposite to the anal. 



The Sharks of the two closely allied families which comprise 

 this suborder show a combination of primitive and specialised 



