CRETACEOUS FORMATIONS. 07 



Wells. Had Cuvier's conjecture, that the extremities of the Mosasaurus resembled 

 those of the Plesioscmrus, been supported by the evidence of such remains of extremities 

 referable to Mosasaurus as have been discovered since his time, the present remarkable 

 specimen from the Chalk Formations of Kent, might have been ascribed with some 

 degree of probability to the great Lacertian of the Maestricht Chalk. But the evidence 

 which has been adduced from the remains of extremities of the Mosasaurus from the 

 Green-sand of New Jersey, in the United States,* is incompatible with the supposition 

 that the phalanges of the Mosasaurus were united by flattened surfaces and syndosmosis. 

 No remains of the Mosasaurus, so far as I know, have been discovered in the Chalk- 

 pit at Burham, but some vertebrae of Plesiosaurus have been obtained from thence, 

 including the fine one figured in T. XIX. In the specimen figured in T. XVII, 

 fig. 1 , three phalangeal bones, and part of a fourth are preserved in one digit, three 

 phalanges in the adjoining digit, and one phalanx of the next, which, if it be in its 

 natural relative position, would belong either to the outermost or the innermost digit; 

 and this is the more likely, as the phalanx of a fourth digit is on the same parallel 

 with the proximal phalanges of the two best preserved digits. In the paddle of the 

 Plesiosaurus the phalanges of the three middle digits are on the same transverse 

 parallel, whilst those of the outer and the inner digits are on a higher or more 

 ' proximal ' plane. 



I conclude, therefore, that the phalanges marked a, m, and iv, are the middle ones 

 of a pentadactyle paddle, and that the phalanx marked v has belonged to either the 

 inner or the outer terminal digit. If the fragment of bone that closely adheres by a 

 flat surface to the proximal end of the phalanx a, belong to the small carpal bone 

 which articulates with the second digit in the paddle of the Plesiosaurus, we must 

 consider the phalanx to which it is attached, and the two parallel phalanges, as 

 appertaining to the proximal series : but that fragment may be a remnant of a 

 proximal phalanx itself. The proximal surface of the three phalanges is slightly 

 concave : the shaft of the phalanx is thick and strong ; rather compressed from before 

 backwards ; gradually contracting to the middle part. Their substance presents a 

 coarse cancellous texture throughout, with the cells or intervals widest at the middle 

 of the bone. The parts being represented of the natural size, it is unnecessary to 

 specify the dimensions of the phalanges. If the length of the proximal phalanx be 

 taken with the compasses in digits Hi and iv, it will be found that the two following 

 phalanges progressively decrease in length. On the supposition that the phalanges of 

 these digits are the first, second, and third, we may estimate the length of the entire 

 paddle, according to the proportions of that of the Plesiosaurus Hawkinsii, at sixteen 

 inches ; which would accord with the proportions of the vertebra of the Plesiosaurus 

 from the same pit, figured in T. XIX. 



* Quarterly Journal of the Geological Society, Jan., 1849, See also, ante, pp. 37 — 39. 



