320 



University of California Publications. 



[Geology 



specimens of M.( ?) atavus described by Fraas, 7 from the middle 

 Trias of Germany, and are set in more or less distinctly separ- 

 ated alveoles. The dentition in several specimens, as appears in 

 figure one adapted from Wiman, is very close to that of PJialaro- 

 don, a Nevada Middle Triassic form recently described 8 by the 

 writer. The teeth of other specimens (fig. 2) are less like 

 Phalarodon and more like Mixosaurus of the Italian Triassic. It 

 seems not impossible that two types are represented in Wiman 's 

 material. 



One of the most inter- 

 esting discoveries made by 

 Wiman is the finding of ex- 

 cellent material represent- 

 ing the limbs and arches of 

 M.(1) nordenskioldii. Both 

 anterior and posterior 

 limbs were obtained in such 

 excellent state of preser- 

 vation that nearly all the 

 essential characters can be 

 determined. In both limbs 

 the epipodial elements are 

 distinctly elongated and 

 separated by a median cleft 

 as in most Triassic ichthyo- 

 saurs, and the phalangeal 

 elements generally show 

 the median constriction, 

 which has been considered 

 as representing a rudimen- 

 tary shaft region. 



The anterior limb (fig. 

 3) is in general much like 

 that of Mixosaurus cor- 

 nalianus of the Italian 

 Triassic. It differs from 



Fig. 3. Mi.rosaurus(f) nordenskioldii 

 (Hulke). Anterior limb, X %. R, radius. 

 (After Wiman). 



i Fraas, E., Iehthyosanrier der Siiddeutsehen Trias-und-Jura-Ablagerun- 

 gen, 1891, p. 38; Taf. 1, figs. 17 and 18, and Taf. 3, figs. 2 and 3. 

 8 Univ. Calif. Publ. Bull. Dept. Geol. vol. 5, p. 382. 1910. 



