I 4 8 



SELACH1I 



FIG. 108. 



Spiral row of teeth of Heliuoprion bessonovi, Karp. ; Permo-Carboniferous, Russia. A, new 

 teeth being formed ; 1J, teeth in use ; C, old teeth passed out of use. (After Karpinsky, from 

 Brit. Mv.s. G-uitle.) 



DIVISION B. 



Only the hyostylic type of jaw attachment is known to occui 

 in these fish. The notochord is always constricted. 



A rostrum is present, generally strengthened by cartilage ; it 

 appears, however, to have been lost in the Squatinidae and 

 Centrobatidae. 



SUBDIVISION 1. 

 Sub-Order 1. SCYLLIOIDEI. 



An anal fin is present and the dorsal fins are spineless. The 

 centra are generally asterospondylous ; concentric calcifications may 

 appear (Cetorhinus), as well as the more usual radial calcifica- 

 tions, but there are generally four radiating wedge-shaped 

 masses of uncalcified cartilage .converging towards the centre from 

 the bases of the arches (Fig. 94). The rostrum is supported by 

 three cartilages, which generally meet at a point in front (Fig. 59, 

 C). The palato-basal articulation is loose, and the process reduced. 

 The teeth remain fairly simple, the median cusp enlarging to a 

 sharp piercing cusp (Sphenodus), or a flattened conical cutting blade 

 (Carcharodon), The spiracle is small, or may be closed up. 



