275 



Cope to Rhamphosaurus, and finally by Professor Marsh to Tylosaurus. A 

 series of specimens belonging to one individual, from the yellow chalk of 

 Kansas, consists of several small fragments of jaws with bases of teeth, a 

 basi-occipital bone, and five vertebras. 



■ The basi-occipital is obliquely distorted, from pressure. It has attached 

 the diverging processes of the basi-sphenoid. The condyle has approximated 

 3 inches in transverse diameter, and is about 2 inches in depth. The diverg- 

 ing processes of the basi-sphenoid, at their conjunction with the basi-occipital, 

 are about 3§ inches wide. The vertebras are all more or less crushed and 

 distorted. One of the specimens, a posterior cervical, has the body below 3 

 inches in length, and the truncated hypapophysis about 1£ inches in diam- 

 eter. The articular ball and socket approximate 2£ inches in diameter. 



In three of the vertebral specimens, of about the same length as the pre- 

 ceding, the hypapophysis is rudimental. The remaining specimen is a more 

 posterior dorsal, and is of nearly the same size as the other vertebras. 



A second series of specimens, belonging to another individual, consists of 

 several much-mutilated cervical centra, small fragments of jaws with bases 

 of teeth, a coronoid bone, a fragment of a quadrate bone, and the end of the 

 pre maxillary. 



The latter specimen, represented in Fig. 12, Plate XXXV, exhibits the 

 peculiar character of the extremity of the muzzle in Mosasaurus and its allies. 

 It forms a solid, conical, osseous prominence, with the end obtusely rounded 

 and projecting beyond the anterior teeth. The sides of the premaxillary 

 toward the end are perforated with large vasculo-neural foramina. The pro- 

 jecting end of the bone extends about 1£ inches in advance of the bases of 

 the first pair of teeth. Immediately in front of the latter there is a small 

 conical process. 



Several specimens of a third individual consist of a caudal vertebra and 

 two teeth, which, from the adherent matrix, have been obtained from white 

 or cream-colored chalk. 



The vertebra is comparatively well preserved, not being crushed nor hav- 

 ing its body distorted, as is so frequently the case in the specimens which 

 have come under my observation. It is from the caudal series without 

 diapophyses or transverse processes, and is represented in Figs. 1, 2, Plate 

 XXXVI. The posterior ball, defined from the body by a narrow ledge, and 

 the anterior cup are nearly circular, with a slight hexahedral disposition. 



