SAUROPTERYGIA 233 



do not therefore separate those with numerous caudal vertebrae, 

 as "Macroura," from those with few or more. The extinct 

 Dolichosaurus of the Kentish chalk, with its proccelian vertebrae, 

 cannot be ordinarily separated, by reason of its more numerous 

 cervical vertebrae, from other shorter-necked proccelian lizards. 

 As little can we separate the short-necked and big-headed 

 aniphiccelian Pliosaur from the Macrotrachelians with which 

 it has its most intimate and true affinities. 



There is much reason, indeed, to suspect that some of the 

 niuschelkalk Saurians, which are as closely allied to Notlw- 

 scuurus as Pliosaurus is to Plcsiosaurtis, may have presented 

 analogous modifications in the number and proportions of the 

 cervical vertebrae. It is hardly possible to contemplate the 

 broad and short-snouted skull of the Simosaurus, with its 

 proportionally large teeth, without inferring that such a head 

 must have been supported by a shorter and more powerful 

 neck than that winch bore the long and slender head of the 

 Notlwsaurus or Pistosaurus. The like inference is more 

 strongly impressed upon the mind by the skull of the Placodus, 

 still shorter and broader than that of Simosaurus, and with 

 vastly larger teeth, of a shape indicative of their adaptation 

 to crushing molluscous or crustaceous shells. 



Neither the proportions and armature of the skull of 

 Placodus, nor the mode of obtaining the food indicated by its 

 cranial and dental characters, permit the supposition that the 

 head was supported by other than a comparatively short and 

 strong neck. Yet the composition of the skull, its proportions, 

 cavities, and other light-giving anatomical characters, all 

 bespeak the close essential relationship of Placodus to Simo- 

 saurus and other so-called " macrotrachelian " reptiles of the 

 muschelkalk beds. I still, therefore, regard the fin-like modi- 

 fication of the limbs as a better ordinal character than the 

 number of vertebrae in any particular region of the spine. Bui 

 by those who would retain the term Enaliosauria for the 



