THE BONES IN THE ENALIOSAUEIA. 309 



tale, but entirely within the parietal bones. The temporal 

 fossae are large in both types. In Satteria the postfrontal is di- 

 vided so as to form a bone like that named postorbital in Lizards ; 

 but in some Ichthyosaurs the postfrontal appears to be divided, 

 as in lizards ; and if so, the temporal fossae are circumscribed 

 by the same bones in Satteria and Ichthyosaurus, and the 

 bones are similarly placed. The nasals of Satteria are rela- 

 tively small, and do not extend over the frontals and between the 

 orbits, nor do the postfrontal and prefrontal bones meet above the 

 orbit, as in Ichthyosaurus. The quadrato-jugal, supraquadrate, 

 and probably the postorbital bones are wanting from the skull 

 of Satteria, as well as the transverse bone. In Satteria the base 

 of the orbit is made by a large turtle-like maxillary, which almost 

 excludes the malar bone. In Ichthyosaurus the malar bone forms 

 the base of the orbit, and entirely excludes the maxillary. Sat- 

 teria possesses an interorbital septum, which does not exist in 

 Ichthyosaurus. The quadrate bone is very unlike that of Ichthyo- 

 saurus in being perforated from back to front, and in sending a 

 long process forward and inward to lap in front of the pterygoid ; 

 and it is jammed in the skull more firmly. 



The palate is not so open as in Ichthyosaurus. And it is ne- 

 cessary to use the " chelonian " interpretation of Ichthyosau- 

 rus to harmonize the bones. The pterygoids of Ichthyosaur 

 would need not to be prolonged anteriorly between the vomers, 

 but only to meet them and allow the vomers to meet mesially. 

 And the premaxillary would not need to be prolonged so far 

 back between the maxillary and vomer to give the ichthyosau- 

 rian palate the essential peculiarities of Satteria, except that in 

 Ichthyosaurus the palatine does not carry teeth. Of course the 

 prenasal part, of the skull does not admit of comparison, any more 

 than do the teeth. 



The vertebrae, though shorter from back to front than in 

 lizards, have the centrum much longer than in Ichthyosaurus ; 

 the neural arches are stronger than in Ichthyosaurus, and diifer 

 in being anchylosed to the centrum. The caudal vertebrae are 

 ossified in two parts in Satteria, so that the suture divides the 

 two cups ; but of this Ichthyosaurus shows no trace. There are 

 median abdominal ribs ; but the costal ribs of Satteria have ex- 

 panded single heads. The apparatus of infracostal ribs seems 

 capable of being moved away with equal entirety in both groups, 

 owing to the union of some of the elements by overlap. The 



