120 University of Kansas Geological Survey. 



In Platecarpus the exoccipital reaches to the margin of the 

 cartilaginous surface of the basioccipital processes on the outer 

 side anteriorly, and is broader here than in Clidastes. 



In Tylosaurus the exoccipital reaches only a short distance 

 downward on the sides of the hypapophyses, while the basi- 

 sphenoid extends much further back on the inner side. The 

 cartilaginous surface at the extremity of the hypapophysial 

 processes seems to be more elongated. 



Exoccipital. 



Exoccipital and paroccipitol of Baur ; exoccipital of Cope. 

 There has been not a little controversy over this element, or the 

 distal part of it, by Professors Baur and Cope, which the reader 

 may follow, if he chooses, in the references given below. 52 Baur 

 holds that the bone called exoccipital by Cope, and which never 

 shows a trace of division in this group, is in reality composed 

 of the conjoined exoccipital and paroccipital. To avoid con- 

 fusion, it will be desirable to give here the different names by 

 which the elements of the cranial bar have been called by 

 different authors in the Lacertilia : 



Paroccipital, Baur. 



Exoccipital, Cope. 

 Squamosal, Gegenbaur, Baur (1892), Merriam. 



Mastoid, Cuvier, Owen. 



Supratemporal, Parker, Baur (1887). 



Opisthotic, Cope (1871)., 



JPar'Occipital, Cope (1892). 

 Prosquamosal, Baur. 



Quadratojugal, Gegenbaur, Baur (1889, 1892), Merriam. 



Squamosal, Owen, Huxley, Parker, Cope (1871), Baur (1887). 



Supratemporal, Cope (1892). 



The element under discussion, whatever be its composition, is 

 usually closely united with the petrosal ( prootic) , the two 

 rarely being found disassociated. The stout suspensorium, 

 composed of these two bones and the squamosal, is directed 

 outwards, somewhat upwards, and backwards, articulating with 

 the squamosal and quadrate. The line of union between the 



52. Baur, Amer. Nat.,1896, pp. 143, 327; Anat. Anzeiger, x, 327. Cope, Amer. Nat., 1895, pp. 855, 

 1003; 1S96, p. 147. 



