388 



University of California Publications. 



[Geology 



slender, indicating that the anterior end was only a few milli- 

 meters in front of this point. The nasal bones extend behind 

 the narial openings for a short distance, but appear not to reach 

 back as far as in other ichthyosaurs. 



The form of the nasals and frontals seems in this specimen 

 to be quite different from that in the typical ichthyosaurians. 

 The structure does not, however, correspond to that in the Tha- 

 lattosauria, as the premaxillaries do not seem to form the prin- 

 cipal portion of the bar between the superior narial openings. 

 It is, indeed, not probable that the posterior ends of the pre- 

 maxillaries reached backward between the narial openings. 



The maxillaries are formed much as in the ichthyosaurs. 

 The premaxillaries appear to be unrepresented. A rather 

 sharply marked groove extending forward across the lateral 

 border of the nasal from the anterior end of the superior narial 

 opening on one side of the skull was probably occupied by the 

 posterior end of a premaxillary having much the same form as 

 in some of the ichthyosaurs. 



AFFINITIES. 



The skull of Phalarodon resembles that in the Ichthyosauria 

 in its general form. It differs from the typical ichthyosaurs 

 in the form of the frontals and nasals, and in the characters of 

 the dentition. The exposed area of the frontals is much larger 

 than in the typical ichthyosaurs, while the nasals seem to be 

 much smaller than in any form thus far described. Not only 

 have the nasals apparently not extended backward over a large 

 part of the frontal region as in Ichthyosaurus and Cymbospon- 

 dylus, but their extension anterior to the narial openings is also 

 much shorter. There seems to be good reason for considering 

 that the premaxillaries were separated posteriorly by the nasals 

 as in the ichthyosaurs and proganosaurs. The lower jaw differs 

 from that of most ichthyosaurs in the shortness of the lateral 

 exposure of the angular element, but in this respect resembles 

 the American Upper Triassic genus Merriamia. In the Italian 

 Mixosaurus the angular also shows a relatively small lateral 

 exposure. 



