﻿CHIM2EKID.2E. 53 



The genera and species of this family are distinguished by the 

 characters of the dentition ; and in the case of most of the extinct 

 forms this is the only part of the skeleton available for study. A 

 convenient nomenclature for the various parts of the teeth has thus 

 been proposed by E. T. Newton l ; and this will be adopted in^ the 

 following pages, except that here the term " tritor " is substitute^ 

 for " tooth." 



Synopsis of Genera. 



A.. Outer tritors of mandibular teeth two (an- 

 terior and posterior). 

 Mandibular tooth with narrow symphysial 



surface, and external thickening along 



the oral border. Palatine tooth with 



deeply cleft posterior border, and the 



tritors in an outer and an inner lon- 

 gitudinal series Ganodus (p. 55). 



Mandibular tooth with narrow symphysial 



surface, and external thickening along 



the oral border. Palatine tooth with 



four tritors, two being inner, one 



median, and one outer ; no posterior 



excavation Ischyodus (p. 59). 



Mandibular tooth with broad symphysia 



surface, and no external thickening 



along the oral border. Palatine tooth 



with three tritors, two being inner and 



one outer ; no posterior excavation . . Edaphodon (p. 73) . 



B. Outer tritors of mandibular teeth absent. 



Mandibular tooth with narrow symphysial 

 surface, and external thickening along 

 the oral border. Palatine tooth with 

 single large tritor divided into two 

 processes anteriorly Callorhynehus (p. 87). 



C. Mandibular teeth thin, with the outer tritors 



small and numerous, and symphysis 

 narrow. 



Mandibular tooth with two rows of dot-like 

 beak-tritors and similar outer tritors ; 

 median tritor absent. [Palatine tooth 

 unknown.] Elasmodeetes (p. 88). 



Mandibular tooth with large beak-tritor, 

 this and the outer tritors being lami- 

 nated ; median tritor present. Pala- 

 tine tooth with four tritors, two being 

 inner, one median, and one outer, the 

 three first with tendency to fusion . . Elasmodus (p. 88). 



1 Chimaeroid Fishes, Brit. Cretaceous Rocks (Mem. Geol. Surv. 1878), p. 4. 



