;U MOSASAURUS. 



hypapophysis ; thirty-eight without articidar processes, but retaining transverse 

 processes ; twenty-six having the hitter, and in addition, facets for chevron bones ; 

 forty-four without transverse processes, and possessing coossified chevron bones; 

 and seven devoid of processes. 



Goldfuss' estimates the number of vertebrae at about one hundred and fifty-seven, 

 which he divides as follows : atlas and axis ; thirteen vertebrae with a hypapophysis; 

 twenty-six witli transverse and articular processes, but no hypapophysis ; thirty with 

 transverse, but no articular processes ; thirty as in the latter, but in addition, pos- 

 sessing chevron bones ; forty-four without transverse processes, but having chevron 

 bones ; and twelve without processes. 



The ribs articulated by their head alone with the ends of the transverse processes. 



The most remarkable character in the anatomy of the vertebral column of the 

 Mosasanrns, is the coossification, in the hinder part of the tail, of the chevron bones 

 with the bodies of the vertebrae, a condition previously known only as a peculiarity 

 of Fishes. The superior and inferior vertebral arches, in association with their long 

 spinous processes, and the absence of transverse processes, indicate the tail of Mosa- 

 saiiruN to have presented the laterally compressed appearance and great vertical 

 depth seen in many Fishes. 



Another remarkable character is the absence, or rather the rudimental state, of 

 the articular processes from about the middle of the vertebral series posteriorly, a 

 condition likewise observed in Cetaceans. 



The characters just given indicate Mosasaurus to have been eminently aquatic in 

 habit. The tail possessed great freedom of movement in a lateral direction as in 

 Fishes. The absence of articular processes in the posterior half of the vertebral 

 series leads to the suspicion that no vertebrae were coossified so as to constitute a 

 sacrum. Perhaps, also, there were no hinder extremities, though these may have 

 existed, without the presence of a sacrum, adapted to swimming, as in Plesiosaurus, 

 with which Mosasaurus exhibits other important points of resemblance, as will be 

 seen hereafter. 



Most of the remains of Mosasaurus which I have had the opportunity of exam- 

 ining have been derived from the Cretaceous Green-sand deposits of New Jersey, 

 in which they are frequently found by those engaged in digging the Gr.-^en-sand, or 

 Marl as it is commonly called, for agricultural purposes. With the exception of a 

 number of well-preserved teeth, the fossils have usually been submitted to me in 

 such a fragmentary condition tliat they haA'e served little else than to indicate the 

 genus or fiimily to which they belonged. I have seen no considerable portion of a 

 skull, though I have met with small fragments of many skulls. Vertebrae, though 

 common, arc usually deprived of all their processes. Bones of the extremities are 

 almost unknown. 



The fossil remains of Mosasaurus, from New Jersey, are usually jet black, or iron- 

 gray, more or less brittle, and impregnated Avith sulphuret of iron. Not unfre- 

 quently the pulp cavities of teeth and hollows of bones are occupied by solid accu- 

 mulations of the latter substance. The decomposition of the sulphuret of iron, 



• Schadelbau, etc., Nov. Act. Acad., Vol. XXI, p. 194. 



