SUB-CLASS I 



SELACHII 



47 



fin low, inuch extended. Skin naked, or with shagreen gramUes. Jurassic to 

 Recent. 



hchyodus, Egerton (Leptacanthus, Ag. ; Auluxacanthus, Sauvage ; Clmnaer- 

 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- 

 angulär, tapering in front, with four tritors ; anterior 

 upper teeth Square, antero- posterior ly compressed. 

 Dorsal fin spine laterally compressed, smooth or 

 longitudinally striated, with a double longitudinal 

 series of denticles on the hinder face. Males with a ' f 



short, arched head spine, bearing a Cluster of denticles _^i«^ ^^i 

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

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

 Lithographie 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. 



^: 



Fio. 93, 



Etlaiihodon'sedqvncki, An. sp. Teeth, 1/2 nat. size. I.ower Chalk ; I.ewes. 

 Hill, Left niaiulibular tooth, inner aspect ; p, Left hinder npper tooth, oral 

 aspect ; V, Ijeft anterior upper tooth, inner aspect ; a, Tritors ; sym, Syni- 

 Ithysial border (after E. T. Newton). 



Fig. S>2. 

 Ischyodua ai'itu^, H. v. Meyer. 

 Almost complete skeleton,* 1/2 

 nat. size. Upper Jurassic 

 (Lithopraphic Stone) ; Eichstädt 

 (after II. v. Meyer). 



Fachymißus, Brachymylus, Sm. Woodw. Upper Jui-assic ; England. 



