AND AVES OF NORTH AMERICA. 



217 



The teeth are, numerous, they are miniatures of those of the Mosasaurus, in most 

 respects. Those of the pterygoids appear to be loss compressed than the mamillaries; all 

 have large pulp cavities, though they are restricted by peripheral ossification, as in other 

 genera. 



The palatines have not united on the median line, and it would appear that they were 

 not in contact. They have a broad Longitudinal groove anteriorly. They have no teeth. 

 The pterygoids are largely developed. They are widest anteriorly; they present a thin 

 free edge externally and a thick reverted margin interiorly; the tooth scries is nearer the 

 outer than the inner margin. The ectopterygoid rises from a strong lateral process of the 

 pterygoid. It represents an obtuse process downwards and a thin process anteriorly. Its 

 position is below the middle of the postfrontal. It is very doubtful whether it had other 

 than ligamentous connection with the maxilliary, as it is far removed from its extremity. 



The vertebrae in this genus are more numerous than in Mosasaurus, while the number 

 of cervicals bearing hypapophyses is less. The caudal diapophyses are reduced to small 

 knobs, and disappear on some of the anterior of those that bear chevron bones. The 

 neural spines of the caudals are much compressed, and have anterior and posterior alee 

 On the distal caudals they become cylindric and fish-like. The zygapophyses become ob- 

 scure, and finally disappear ; before doing so the posterior acquire an up rather than a 

 down-looking' face. 



The centrum of the atlas is entirely below the very large processus odontoideus. It 

 is keeled below, and has less contact with the condyle than lias the processus; the latter 

 is free from the axis, which resembles other cervicals. The odontoid ring i s not closed 

 above. Tin- neurapophyses of the atlas arc; continuous with the lateral segment of the 

 centrum which furnishes articular faces to the basal segment, the odontoid, and to the occi- 

 pital condyle, and sends a, process back alongside the axis. The neurapophyses are slen- 

 der; if they have a, neural spine, it is lost. They arc-, on the whole, much as in Mosasau- 

 rus, and. in Va.ra.nus. 



The ribs commence immediately behind tin 1 atlas, if the forms of the diapophyses and 

 their articular surfaces arc; to be relied on. The diapophysis of the axis is nearly horizon- 

 tal, descending a, little anteriorly ; the posterior portion of its extremity is subtruncate 

 for articulation to a. small rib. The same part of the diapophysis of the third is more 

 prominent, is ovate, and continuous with a subhori/.onfal ridge with articular-like surface, 

 which extends to the rim of the cup. The fourth is similar, but the articular faces are 

 more similar in widths and lengths. The inferior limb becomes regularly shorter and less 



horizontal posteriorly. From the eighteenth to the twenty-third tin; surfaces are a little 

 smaller, and without apparent difference in size and form. The rib-bearing surfaces pos- 

 terior to this point are lost. 



AMERICA. PHILO. S00. — VOL. XIV. f). r >. 



