22 CALIFORNIA ACADEMY OF SCIENCES 



a small foramen is seen near the distal end of the pectoral ridge. Although 

 it is quite small it probably represents an epicondvlar foramen. 



Tlic humerus of T. shasfenfiis (PI. viii, fig. <S) is perhaps a little more slender 

 than ill T. alexartdrae, Init is imperfectly rejiresented in the figures, as it is 

 considerably weathered. 



The radius (VI. viii, fig. o) is shafted, but shows considerable <listal and 

 proximal expansion. Its length is about one half that of the humerus. The 

 ■uhta (I'l. wii, figs. () and 7) is convex posteriorly and concave anteriorly, show- 

 ing no median constriction. 



Several rounded ossicles resembling the phalanges of Bapfaaodon have been 

 found associated with the limb and arch bones of the type specimen. Undoubtedly 

 they represent carpals or })lialaiiges, and there is a possibilitv that some at least 

 are phalangeal elements. 



The fyi^e nf limb represented in this form is that of an aquatic animal, as is 

 shown particularly in the extreme shortening and broadening of the humerus 

 and of the ('}>ipodial liones. Such indications as are given in the possible char- 

 acter of the phalanges would also point in this direction. The specialization of 

 the lindi is greater than that in the I'roganosauria, ( -horistodera or Parasuchia. 

 It can perhaps be best compared with that of the Plesiosaurs or with the Triassic 

 Ichthyosaurs. The humerus is, however, a little more slender medially than in 

 the Ichthyosaurs. If tin- rounded ossicles are really phalanges, it is evident 

 that the limb was no longer serviceable to any extent for land or shore locomo- 

 tion but had become the specialized paddle of a purely aquatic type. 



HABITAT, LOCOMOTION, FO(JI). 



The remains of Thalattosaurs are known only in purely marine deposits 

 containing little or no material of terrestial origin. They are associated with a 

 fauna consisting of numerous forms, both vertebrate and invertebrate, which 

 are not known to have existed away from marine areas. In the structure of the 

 skeleton we find the abbreviated and broadened proximal segments of the limbs, 

 the slender snout with prehensile terminal teeth, and the median superior nares, 

 indicating a j^urely aquatic type. There can scarcely be room for doui)t that 

 the Thalattosaurs as a group were typical marine forms. 



The larger and more specialized species comprised in the genus Thalaito- 

 saurus were strictly ]iatatory. They may have visited the shore but, like the 

 Plesiosaurs, were better fitted for swimming than for crawling. Of the smaller 

 Nectosmirus we unfortunately do not know the limbs. They ma}' have been con- 

 siderably less specialized than in the other genus, and the animal to a corre- 



