COMPARISON OF DENTAL PLATES. 



121 



continued along the floor and sides of the pharynx. In Rhinochimaera, on the 

 other hand, the dental plates have become thin and have developed hard cutting 

 edges, giving the mouth an almost beak-like appearance. In the plates tritoral 

 areas are reduced to thread-like elements, so delicate that they become difficult to 



94* 



Fig. 94. Dental plates, and roof and floor of mouth of : A, B, Harriotta raleighana. C, D, RhinocHimaera pacifica. 



distinguish even in the hard anterior pair of "vomerine" plates; and in con- 

 nection with the obsolescence of the tritoral areas, it is now interesting to observe a 

 great reduction in the number and size of the papillae of the mouth. Thus on the 

 roof of the mouth there occur no papillae throughout the wide tract immediately 

 behind the palatine plates. 



