﻿KIMMERIDGE CLAY. 



57 



The shaft at its narrowest part presents in section the form given in fig. 5, PI. XVII, 

 being almost flat, palmad, and convex anconad transversely. It soon begins to expand 

 into the distal end of the bone. The crest, e , simulates the ' supinator ' one in Mammals, 

 and is not perforated, as is the answerable disto-radial crest in some existing Sauriaris. 

 Such perforation is very small in Varanus (PI. XVII, fig. 6, e). There is no indication of 

 this vascular or nervous canal in Omosaurus, and the crest is relatively shorter than in 

 Varanus. The ulnar expansion,/, of the distal end is thick and tuberous. 



Sufficient of the radial condyle, ff , remains to show its Saurian extension palmad, and 

 its convexity in Omosaurus (ib., fig. 4) ; the precise form and extent of the less prominent 

 ulnar condyle or trochlea is not definable. 



The texture of the shaft of this humerus, as exposed by the fracture across its middle 

 narrowest part, is compactly dense ; there is a small medullary cavity (fig. 5) which 

 seems to have but a short longitudinal extent. 



A deep anconal depression (ib., fig. 2, i), marks that aspect of the distal expansion in 

 a greater degree than in any Crocodilian, Lacertian, Dinosaurian, or Pterosaurian 

 humerus that, as yet, has come under my notice ; it gives to this part of the humerus of 

 Omosaurus something of a Mammalian character. 



The following are admeasurements of the humerus : 



Length 



Breadth across radial or pectoral crest 

 „ distal end . 

 „ ,, middle of shaft 



Girth of 



Length of base of radial or pectoral crest 

 „ ulnar crest 



Ft. Is. Lines. 

 2 9 

 1 G 



110 



5 6 

 ICO 



1 4 

 8 



The figures of this bone on PI. XVII are reduced to one fourth of the natural size. 



Although I should have hesitated to found a genus or generic term on a solitary 

 limb-bone if such distinction had not been supported by the vertebral characters, yet the 

 features were so much more strongly marked in the present than in previously described 

 or figured humeri as to have afforded a better excuse for such taxonomic deduction, which 

 ought to rest, and, as a rule, can only safely do so, on characters afforded by associated 

 parts of the skeleton or teeth. 



Mutilated as are the humeri discovered with unquestionable vertebrae of Cetiosaurus 

 longus in the Geological Museum of Oxford, justifying the conclusion that they belonged 

 to the same individual, they are unmistakably distinct in character from that bone in 

 Omosaurus. 



Although the radial or pectoral ridge be broken away in the subjects of figures of the 



