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University of California . 



[Vol. 3. 



broad and each shows a marked median constriction, the notches 

 being very deep on the inner side. The tibia is somewhat broader 

 than the fibula. 



The tibiale is imperfectly preserved. The anterior margin is 

 not shown and it is not possible to determine whether it was 

 notched. The intermedium is imperfect as is also the fibulare. 

 It is not possible to state whether the latter was notched on the 

 posterior side. Distal tarsal two is well preserved and has entire 

 margins. Distal tarsal three is deeply notched posteriorly. In 

 the metapodial region numbers two and three are preserved. 

 Like the corresponding element of the anterior limb, number two 

 has entire margins. Number three shows a deep median con- 

 striction like that in number one of the correspoding region of 

 the anterior limb. 



In the phalangeal region, the arrangement and form of the 

 elements is much the same as in the anterior limb. The rudi- 

 mentary fourth digit is represented by four small ossicles situated 

 immediately behind the mesopodial and metapodial regions. 



Measurements. 



Femur 



Width of distal end *30 



Width of narrowest portion of shaft 18 



Tibia 



Length 19 



Width Hi 



Distal tarsal three 



Length t) 



Width 7 



Metatarsal three 



Length 7 



Width 5.5 



Skull (PL 23, figs. 1, 2, and 3.)— Of the cranial portion only 

 the maxillary, jugal, lachrymal, and postorbital are preserved in 

 such form that they can be satisfactorily studied. The relations 

 of these elements are not markedly different from those in 

 Ichthyosaurus. In a cross-section of the middle portion of the 

 skull as it appears on this specimen there are two palatal bones, 

 probably the palatines and a median element having the appear- 

 ance of the vomer. In each orbit there is a large portion of 

 a sclerotic ring composed of plates of considerable size. 



*Approximate. 



