HYPOSAURUS. 21 
reptile allied to Mosasawrus, and named LHolcodus acutidens, in part at least, appear 
rather to belong to Hyposazwrus. Of the specimens, which Dr. Gibbes has submitted 
to my inspection, that from New Jersey, I think, undoubtedly belongs to the last 
mentioned genus. The other specimen, from the Cretaceous formation of Alabama, 
though agreeing in its form and proportions with the teeth above described, may, 
nevertheless have belonged to a Mosasaurus. 
The collection of the Academy contains a dorsal vertebra, represented in Figs. 
6, 7, Plate IV, from the Green-sand of Burlington County, N. J., which has the 
same form and proportions as the corresponding vertebrae above mentioned, but is 
smaller. ‘The specimen probably occupied a more anterior position in the series ; 
though it may have belonged to a smaller species of the genus. The cabinet of the 
Academy also contains the body of a dorsal vertebra, from the Green-sand of New- 
castle County, Del., which has the same form as the Burlington County specimen, 
but is the fourth of an inch longer. 
Since writing the foregoing I have received for examination a small collection 
of remains of Hyposaurus, belonging to Rutger’s College, New Brunswick, N. J. 
The specimens were sent by Prof. Cook, who informs me that they were obtained 
from a marl pit, at Tinton Falls, Monmouth County, N. J. The specimens have 
the same friable character as those previously described, and they appear to have 
belonged to two different individuals: one quite young, the other of maturer age. 
Those of the young individual consist of several fragments of the occipitals, a 
cervical rib resembling those of the Mississippi Alligator, and the body of a posterior 
dorsal two inches long. Those of the maturer animal consist of a posterior cervical 
and a fourth dorsal vertebra, the bodies of three posterior dorsals, and the shaft of 
a femur. 
The posterior cervical, represented in Fig. 2, Plate IV, corresponds in size, form, 
and details of structure with those previously described. The length of its body, 
which is slightly more concave posteriorly than anteriorly, is three inches, and the 
length of the specimen between the anterior and posterior articular processes is 
three inches and three-quarters. The hypapophysis, somewhat mutilated, appears 
not to have been proportionately better developed than the corresponding processes 
in the cervical series of the Mississippi Alligator. 
The fourth dorsal vertebra, Fig. 3, Plate IV, has lost one-half of its vertebral 
arch with the spinous process, and the other half of the arch is separable at its 
suture with the body. ‘The latter is two inches and a quarter in length below 
and two inches and a half at its junction with the arch. The two ends are nearly 
equally concave, and between them there extends a broad laminar hypapophysis, as 
represented in the specimens upon which Prof. Owen proposed the genus, but as in 
these, unluckily the process is broken so that we are unable to determine its length. 
The bodies of the three posterior dorsals are rather over two inches in length, 
and exhibit the sutures from which the vertebral arches have been detached. They 
are more concave anteriorly than posteriorly, in this and other characters agreeing 
closely with those previously described. 
The shaft of a femur corresponds closely with that already described both in size 
and form, 
