THE REPTILIAN CLASS OF THE MOSASAURIDJE. 



695 



production of its upper and middle part into a long and slender- 

 pointed process (fig. 14, 22'), which terminates by wedging itself more 

 or less deeply between the nasals (ib. is). This structure is associated 

 with a more backward position of the external nostrils (n, n) than 

 in Ophidia, the degree of retrogradation being in proportion to the 

 length of the nasal process of the premaxillary. Thus the charac- 

 teristic process is longer and the external nostrils are placed further 

 back in Varanus and Monitor than in Amblyrhynchus and Iguana ; 

 and in this respect, as in some others indicated by Cuvier, Mosa- 

 saurus (fig. 15) is nearer akin to the Monitors than to the Iguanians. 



Fig. 15. 



Leiodon. 

 Upper surface of skull. 



Mosasaurus. 

 The bony palate. 



Cuvier has rightly represented the backward position of the external 

 nostrils in the Mosasaurus Hoffmanni, but does not refer to the ante- 

 rior boundary of the right aperture, which is clearly and correctly 

 shown in his plate (pi. xviii. fig. 1). 



In the same figure is shown the nasal process of the premaxillary, 

 forming the upper border of that part of the divided nostril. The 



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