84 



University of California. 



[Vol.. 



Judging from a comparison of the limbs with the middle 

 doi'sal vertebrae, it would appear that the posterior limbs were 

 smaller and less specialized than the anterior. 



/Skull. — The posterior half of a cranium belonging to an 

 undoubted representative of Shastasaurus was found with the 

 type specimen of alexandrce (Pis. 12 and 13). This skull is 

 typically Ichthyosaurian in nearly every particular. The small 

 frontal s are overlapped anteriorly by very large nasals. The 

 superior portions of the parietals form a narrow ridge in which 

 is a parietal foramen. The orbit is of enormous size, and 

 the structure of its bony rim, as also that of the single tem- 

 poral arch, is similar to that in Ichthyosaurus! The form of 

 the jugal, lachrymal, and the prefrontal, is essentially as in 

 Ichthyosaurus . The postfrontal meets the prefrontal above the 

 middle of the orbit and considerably in advance of the temporal 

 opening. The upper portion of the postorbital extends back- 

 ward beneath the supratemporal and squamosal, which are 

 partly broken away from this specimen. The quadratojugal is 

 missing or moved from its natural position. The quadrate is of 

 the Ichthyosaurian type. The end of the maxillary is present 

 but is unfortunately broken off behind the posterior teeth. The 

 otic bones, the supraoccipitals, and the lateral occipitals could 

 be only partly exposed and their relations cannot be definitely 

 determined. Sclerotic plates like those of Ichthyosaurus appear 

 in both orbits. 



On the lower side of the cranium the pterygoids and palatines 

 have been well exposed and are similar to these elements in 

 Ichthyosaurus longifrons, as figured by Owen. Portions of what 

 are probably the basioceipital and basisphenoid and one of 

 the quadrates are also shown. Close to the pterygoids there is 

 present on each side a long rod-like bone, representing the 

 thyrohyal of Owen, such as has been described by him from 

 I. tcnuirostris. Considerable portions of both rami of the 

 mandible are present. The break at the anterior end of the left 

 ramus shows the dentary, splenial, supra- angular, and angular. 

 The splenial extends the whole height of the jaw at this point. 

 The portion of the dentary shown is the thin posterior end 

 supported by the supra- angular. The angular is hidden on the 



