10 PEOF. HUXLEY ON THE SPECIFIC AND GENERIC 



sternum. Each of the vertebral ribs from the tenth to the seventeenth 

 vertebrae inclusively, on the other hand, is united with the sternum, 

 or its continuation, by two such semieartilaginous costal elements, 

 which may be respectively termed sternal and lateral. The sternal 

 elements of the ribs of the tenth and eleventh vertebrae are united 

 with the sternum proper ; those of the next five vertebrae are con- 

 nected with its median backward prolongation, while those of the 

 seventeenth vertebra are attached to the processes into which this 

 prolongation divides posteriorly. 



The sternal costal elements are very broad and flat, and though 

 the lateral ones are less so, they are wide and expanded. The 

 lateral costal pieces of the eleventh to the sixteenth vertebrae 

 inclusively, give attachment to very large and flat, triangular, pro- 

 cessus tincinati. Those of the twelfth are 3-f- inches long and If 

 inch wide at their widest part. The transverse processes of the 

 twentieth vertebra bear rudimentary ribs. The centrum of the 

 thirteenth vertebra is 1^ inch long, and the vertebra is 3|- inches 

 high from the lower edge of the centrum to the summit of the 

 neural spine. The centra of the vertebrae retain nearly the same 

 length to the twentieth caudal; but behind tliis vertebra they 

 are shorter, as are the anterior dorsal vertebrae. The first caudal 

 vertebra is provided with two styliform bones, which represent the 

 chevron bones of the other caudal vertebrae, but are not united 

 below. 



The dorsal scutes have the arrangement which has often been 

 described. They are separated (except perhaps the median rows) 

 by integumentary spaces, neither overlapping nor uniting by 

 sutures ; and there are no ventral scutes. 



Among the osteological characters which have been detailed, the 

 peculiarities of the tergal armour, the proportions of the skull, 

 combined with the characters of the ridges upon its surface, and 

 the form of the premaxillo-maxillary suture amply sufiice to dia- 

 gnose this species. Even in the small skull, only 5^ inches long, 

 lent to me by Dr. Gray, the characteristic features of the species 

 are well exhibited, although age appears to give rise to many dif- 

 ferences. Thus the posterior margin of the external nostrils does 

 not extend so far back as in the advilt, and the facial is smaller in 

 proportion to the syncipital region, whose anterior and posterior 

 transverse dimensions are very nearly equal. The orbits are pro- 

 portionally larger, the interorbital space more excavated ; and the 

 outer straight margins of the supratemporal fossae are parallel with 

 the longitudinal axis of the skull. Still more important differoncetf 



