a4 MOSASAURUS. 
hypapophysis; thirty-eight without articular processes, but retaining transverse 
processes ; twenty-six having the latter, 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 vertebre at about one hundred and fifty-seven, 
which he divides as follows: atlas and axis; thirteen vertebra with a hypapophysis; 
twenty-six with 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 
Mosasaurus, is the coossification, in the hinder part of the tail, of the chevron bones 
with the bodies of the vertebra, 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 M/osa- 
saurus 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 vertebra 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 Green-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 that they have served little else than to indicate the 
genus or family to which they belonged. I have seen no considerable portion of a 
skull, though I have met with small fragments of many skulls. Vertebre, though 
common, are 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 with 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, 
ca 
1 Schidelbau, etc., Nov. Act. Acad., Vol. X-XI, p. 194. 
