MOSASAURUS. 43 



postero-inferiorly, is thicker than the former, and exhibits strong marks for mus- 

 cular attachment. 



The distal extremity of the bone expands to about twice the breadth of the middle 

 of the shaft. It is almost flat in front, moderately convex behind, and terminates 

 in a thick angular border, which, though somewhat mutilated, has the appearance 

 as if it had formed a fixed or immovable joint with the bones of the forearm. 

 The measurements of the specimen are as follows : — 



Indies. Lines. 

 Extreme length of the specimen in its present state . , . .10 



Breadth of shaft at middle 1 H 



Thickness of shaft at middle ........ 1 2 



Breadth at tuberosities, estimated ....... 6 



Diameter of head .......... 1 8 



Breadth at distal end ......... 3 8 



Thickness at distal end 1 2 



A fragment of a huge bone, from the Green-sand of Burlington County, N. J., con- 

 tained in the cabinet of the Academy of Natural Sciences, is represented in Figs. 

 3, 4, 5, Plate VIII, rather less than one-third the diameter of the original. The 

 specimen has been usually viewed as the proximal extremity of the humerus of an 

 enormous Turtle, and even Agassiz was impressed with the same idea, for it is the 

 fossil characteristic of his Atlantochelys Mortoni} It bears a resemblance to the 

 corresponding portion of the humerus just described, and probably belongs to the 

 gigantic Mosasaurus. 



The shaft, broken across near its middle, appears of exceeding narrowness in 

 comparison with the breadth of the bone at the tuberosities, and, indeed, is much 

 narrower in this respect, relatively, than in the humerus above described. From 

 this character alone we have good reason to suspect that the two specimens indicate 

 a small and a large species of Mosasaurus. 



The broken end of the bone, under immediate examination, presents an ovoidal 

 section, with the greater diameter thirty-four lines, the shorter twenty-nine lines. 

 The shaft contains no medullary cavity, but is occupied by an interior coarser ossific 

 structure. The upper or front part of the shaft, as in the preceding specimen, 

 exhibits a rough, tuberous surface for muscular attachment. 



The head is ovoidal in outline, fifty-three lines in its antero-posterior diameter, 

 and forty-four lines in its .short diameter. 



The breadth of the bone, from the summit of one tuberosity to that of the other, 

 is eleven inches. The greater tuberosity projects three inches proximaUy beyond 

 the head, increasing by so much the length of the bone. It is compressed antero^ 

 posteriorly, is convex and rough at the summit ; measures four inches wide at its 

 middle, and twenty-six lines thick. The smaller tuberosity, irregular in form and 

 much roughened for muscular attachment, measures forty-one lines in thickness. 



The length of the fragment, from the summit of the greater tuberosity to the 

 broken end of the shaft, is eleven inches. 



Proc. Acad. Nat. Sci. 1849, 169. 



