106 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA. 



to some extent. In the rostral region the preniaxillaries are sculptured so as 

 to produce a peculiar roughened surface. 



The maxittaries are longer in specimen 9950 than in any other described 

 ichthyosaurian, both in relation to the length of the cranium and to that of the 

 rostral region. Almost if not quite half of the dentigerous margin of the upper 

 jaw is situated on these elements. A large lachrymal is clearly defined on this 

 and other specimens. In specimen 9954 it reaches forward to the posterior 

 border of the superior nares. 



The nasals are large and extend back over the frontals almost to the pineal 

 foramen. 



In the frontal region of Cymbospond-ylus the nasals seem to cover as large a 

 portion of the frontal element as in Ichthyosaurus. This might be suspected to 

 be due in part to the displacement of the very thin posterior edges of the nasals, 

 but the area exposed in preparation is probably nearly normal, since in several 

 specimens prepared the border has always exhibited the same characteristically 

 marked outline. 



In contrast to the situation in Ichthyosaurus the large pineal foramen is 

 surrounded mainly by the parietal instead of wholly or in a large part by the 

 frontals. A prominent crest rises rapidly behind the anterior ends of the pa- 

 rietals reaching a very considerable elevation above the middle of the superior 

 temporal openings. The pineal foramen is situated in the anterior portion 

 of this crest, where it occupies such a position that it is directed partly upward 

 and partly forward. 



One of the most striking features of the skull in specimen 9950 (see pis. 2 

 and 6) is the relatively small size of the orbit, as compared with that of the 

 later ichthyosaurs. The orbit as it appears in plate 2 is very slightly depressed, 

 but the amount of overlap of the broken upper end of the jugal amounts at 

 most to not more than twenty-five millimeters or a little more than one-sixth 

 of the height of the orbit. In another specimen (no. 9913, see pi. 6) crushed 

 laterally so that the height of the orbit would tend to be increased, the size 

 of the orbit is also relatively small. In specimen 9950 the anteroposterior 

 diameter of the orbit is about one-sixth the length of the skull, in spite of the 

 fact that the rostral region is relatively short. In Baptanodon as figured by 

 Gilmore" (see also fig. 5) the length of the orbit is only a little less than one- 

 fourth that of the whole skull including the much elongated snout. The 

 relative size of the orbit is particularly noticeable in comparison with the an- 

 teroposterior diameter of the lateral temporal region. The anteroposterior 

 diameter of the lateral temporal area equals about 83 per cent, of the fore and 

 aft diameter of the orbit in Cymbospondylns (no. 9950) ; in Baptanodon it 

 appears to be less than 25 per cent. 



o Gilmore, 0. W., Mem. Carneg. Mus., vol. 2, pi. 8. 



