156 



structure of the interior angle as in the intermaxillaries, of the re- 

 mainder as in the upper maxillaries ; position of the plates more or 

 less oblique. 



(2.) Elasmodus {eXaajia lamina, olovs dens). 



Two maxillary and two intermaxillary plates in the upper jaw ? 



Two maxillary plates in the lower jaw ; lower maxillary thick and 

 strong ; tubercle single, composed of a dental substance resembling 

 in structure a tritor of Psammodus ; in advance of the tubercle the 

 tooth is composed of several series of laminae, arranged in juxta- 

 position and inclined downwards and outwards ; behind the tubercle 

 the dental edge is notched, in consequence of a columnar structure 

 pervading this region of the tooth. The outer surface is enveloped 

 by a coat of dentine. 



A single* specimen in the Hunterian collection aiFords the type of 

 a third genus. 



(3.) Psaliodus {\lia\\s forfex, and ohovs dens). 

 Upper jaw ? Two maxillary plates in the lower jaw. Lower max- 



* Chimseia greenovii, Agassiz. 



f Chimsera hunteri, Owen. 



