CRETACEOUS FORMATIONS. 37 



only, for he says the immediate comparison of the bones themselves would hardly 

 suffice, so great is the diversity and so small the precision of the forms of those 

 bones in reptiles.* 



M. Pictet, in the second volume of his 'Traite Elementaire de Paleontologie,' 8vo., 

 1845, terminates his brief summary of the characters of the Mosasaurus, by stating: — 

 "Les membres paraissent avoir ete termines par des nageoires aplaties," (p. 62.) 



In the collection of Saurian fossils submitted to me by Professor Henry Rogers 

 were some bones of the extremities, showing the Lacertian type of structure, and 

 agreeing in colour, petrified condition, and proportional size with the vertebrae and 

 teeth of the Mosasaunis from the same Green-sand formation. They were too large to 

 be attributed to the Crocodilian species indicated by the vertebrae from the same 

 formation. I subjoin, therefore, a brief description of these interesting fossils which 

 appear to me to throw additional light on the structure of the locomotive organs of 

 the Mosasaurus. 



The first of these bones gave the following dimensions : — 



Feet. Inches. 



Extreme length 2 8 



Extreme breadth of the broader end ..... 8 



Breadth of narrower end of the same bone (imperfect) . . 4^ 



The best preserved extremity of this long bone is expanded and subcompressed, 

 like the lower end of the fibula of the Varanus, one part of this extremity being pro- 

 duced into an obtuse angle. The extremity is smooth, slightly concave transversely 

 on one side, more irregular on the opposite side, with a thick prominent border 

 opposite to the produced angle. The shaft of the bone has an irregular full, oval, 

 transverse section with dense walls of concentric plates of bone, eight or nine lines 

 thick, surrounding a medullary cavity, one inch nine lines in diameter. The shaft 

 is very slightly bent. The opposite extremity which gradually expands, preserving 

 the general form of the shaft, exhibits a strong longitudinal ridge of six inches in 

 extent, but which subsides before it reaches the articular end. Only a portion of this 

 end is preserved, which is slightly and irregularly convex. 



The second long bone of the extremity yields the following dimensions : — 



Feet. Inches. 



Extreme length 2 5 



Breadth round the upper (?) articulating surface ... 4\ 



Depth of articulating surface ...... 3^ 



Breadth of lower (?) end (imperfect) 3 



This bone, therefore, equals in length the preceding, but becomes more attenuated 

 in the middle than any of the long bones in the existing Saurians ; one extremity is 



* Loc. cit., p. "ibT. 



