ABSTEACTS AND DISCUSSIONS OF PAPERS 171 



REGENT STUDIES ON SKULL STRUCTURE OF THALATTOSAURUS 

 BY JOHN C. MERRIAM AND CHARLES L. CAMP 



(Abstract) 



The peculiar marine reptile Thallattosaurus from the Upper Triassic of 

 northern California has been known by very limited materials. A recently 

 exposed skull illustrates several points of structure better than the type speci- 

 men. Fragments representing the rostral region indicate the necessity of a 

 small modification in the first reconstruction. 



REVIEW OF THE PLEISTOCENE SPECIES, PAVO CALIFORNICUS 



BY LOY r E HOMES MILLER 



(Abstract) 



Presence of additional material, both of the fossil form and of the nearer 

 related living species, makes review of the entire question of relationship 

 proper. The Yucatan turkey, Agriocliaris, has been distinguished generically 

 from the northern form, Meleagris. The Central American bird shows certain 

 peacock affinities in the tail feathers and in the osteology of the posterior limb. 

 The fossil species from Rancho La Brea displays characters far removed from 

 Meleagris and intermediate between Agriocliaris and Pavo, but well removed 

 from either genus. A new generic designation for the Pleistocene species be- 

 comes necessary. Chapman considers the present habitat of Agriocliaris the 

 focus of retraction of a larger distributional area. Admitting the possibility 

 that a similar change has taken place in the distribution of Pavo on the 

 opposite side of the Pacific Ocean, it is not surprising to meet with an inter- 

 mediate form in the Pleistocene of California. 



HIPPARION-LIKE HORSES OF THE PACIFIC COAST AND GREAT BASIN 



PROVINCES 



BY JOHN C MERRIAM 



(Abstract) 



Until recently the Hipparion group has been very imperfectly known from 

 North America west of the Wasatch Range, the only described forms clearly 

 of this type being two species reported from the later Tertiary of the John Day 

 region of eastern Oregon. Within the past few years a number of new repre- 

 sentatives have been discovered at widely different localities, and nine or ten 

 species are now known. As the history and distribution of the group have 

 unusual importance in comparative study of the American Tertiary faunas 

 west of the Wasatch, the writer has essayed to assemble the available infor- 

 mation relating to the forms of this genus known in the Pacific Coast and 

 Great Basin provinces. 



