Cope.J 254 [January 20, 



19. The anterior limbs ai"e fins, with all the elements in a single 

 plane, the radius incapable of rotation. The himierus broad and 

 flat. 



20. There are probably no hind limbs. 



Of the above characters the first ten are those of serpents; the 

 five characters following are lacertilian, while the seventeenth and 

 eighteenth are peculiar, and not found in any existing order of rep- 

 tiles. The eighteenth is characteristic of the Sauropterygia. 



The characters of the teeth are much like those of serpents, and 

 resemble much less those of any saurians, since they are without 

 true dentinal fangs; for the ossification of the pulp, which produces a 

 fang-like sujjport to the crown, is only a subordinate character, like 

 that of ossification or non-ossification of cartilages within many exist- 

 ing families. The pterygoids which are in contact immediately in 

 Mosasaurus, are largely free in CUdastes, where they bear teeth as 

 abundantly as do any serpents. Among the Lacertilia the dentition 

 is either truly rhizodont (the Acrodonta) or pleurodont. The teeth 

 of the Varanidag are especially different from those of the present 

 order, and, present only a modification of the pleurodont character. 

 The outer parapet of the jaw is low, and the shanks proportionately 

 short; they are, in addition, more expanded than in most other 

 pleurodont families. 



The characters presented by the temporal region are highly 

 peculiar, and important in determining the affinities of the group. 

 The discovery of its structure furnishes the desired explanation for 

 sundry enigmatical bones which occur not unfrequently in our cre- 

 taceous formations. In the following diagnoses the present is com- 

 pared with the three orders, to which it makes nearest approach. 



Tentudinata. Opisthotic distinct, closely united to exoccipital, 

 squamosal and prootic, and supporting squamosal and quadratum. 



Lacertilia. Opisthotic distinct, closely attached to parietal arc, 

 and at extremity to exoccipital and prootic ; supporting squamosal 

 and quadratum. 



Pythonomorpha. Opisthotic distinct, not, or scarcely in contact 

 with parietal arc, embraced at one end by prootic and exoccipital, 

 and supporting squamosal and quadratum. 



Ophidia. Opisthotic distinct, attached only to prootic, and sup- 

 porting only quadratum. 



There can be no doubt that the suspensorium of Mosasaurus is 

 homologous with the element in the tortoises called by Huxley opis- 



