HYPOSAURUS. 21 



reptile allied to Mosasaurus, and named Holcodus acutidens, in part at least, appear 

 rather to belong to Hyposaurus. 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 vertebree 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 obtaiued 

 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 AUigator, 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 AUigator. 



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 xmable 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. 



