470 



Geological Society. 



one in advance, one on the outer margin, and two side by side near 

 the base, the larger one occupying the inner position ; structure of 

 the tubercles coarse and tubular ; the remainder of the teeth fibrous 

 and bony. Lower maxillaries : large and broad, formed for crushing 

 rather than cutting ; two tubercles, one at the heel, the other in ad- 

 vance ; symphysis broad ; the base invested by the membrane of the 

 mouth, the crown by a coat of hard enamelloid dental substance ; 

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

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

 less oblique. 



(2.) Elasmodus (eXoo-fta lamina, o^ovs 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. 



Chimsera Greenovii, Agassiz. 



f Chimaera Hunteri, Owen. 



