SUB-CLASS I 



SELACHII 



47 



fin hue, much extended. Skin naked, or with shagreen granules. Jurassic to 

 Recent. 



Ischyodus, Egerton (Leptacanthus, Ag. ; Auluxacanthus, Sauvage; Chimaer- 

 acanthus, Quenstedt), (Fig. 92). Lower dental plates 

 rhomboidal, with a narrow symphysial facette ; upper 

 part of outer face covered with a thick layer of 

 dentine, and oral margin sharp ; four rough punctate 

 tritors present. Posterior upper dental plates tri- 

 angular, tapering in front, with four tritors ; anterior 

 upper teeth square, antero -posteriorly compressed. 

 Dorsal fin spine laterally compressed, smooth or 

 longitudinally striated, with a double longitudinal 

 series of denticles on the hinder face. Males with a 

 short, arched head spine, bearing a cluster of denticles 

 at the end. Nearly complete skeletons of /. avitus, 

 Meyer sp. (Fig. 92), and /. quenstedti, from the 

 Lithographic Stone of Bavaria. Detached teeth 

 from the Bathonian (Stonesfield Slate) to the Upper 

 Cretaceous of England, France, Germany, and Switzer- 

 land ; also from Cretaceous of Amuri Bluff, New 

 Zealand. 



Ganodus, Ag Dentition as in Ischyodus, but 

 posterior upper dental plate deeply excavated 

 behind, with a double longitudinal series of numer- 

 ous small tritors. Bathonian (Stonesfield Slate), 

 England. G. oweni, Ag., and other species. 



Fig. 93. 



Edaphodon sedgvncki, Ag. sp. Teeth, ' ■_• nat. size. Lower Chalk ; Lewes. 

 ni'l, Left mandibular tooth, inner aspect; p, Left hinder upper tooth, oral 



aspect; r, Left anterior upper tooth, inner aspeel : a, Tritors; sym, Sym- 

 physial border (after E. T. Newton). 



Ischyodus avitus, H. v. Meyer. 

 Almost complete skeleton, !/ 2 

 nat. size. Upper Jurassic 

 ( Lithographic Stone) ; Eichstadt 

 (after II. \. Meyer). 



Pachymylus, Brachymylus, Sm. Woodw. Upper Jurassic ; England. 



