420 



University of California. 



[Vol. 3. 



The type specimen (No. UU Pal. Mus. Univ. Cal.) was 

 found m the Trachyceras beds of the Hosselkus limestone in the 

 Upper Triassic of Shasta Comity. It includes the anterior two- 

 thirds of the skull and a portion of the temporal region; also 

 parts of over thirty vertebrae, numerous fragmentary ribs, the 

 principal elements of the pectoral and pelvic arches and a 

 considerable portion of an anterior limb. 



Fig. 1. Thalattosaurus alexandrar. Inferior side of the anterior 

 portion of the cranium. M, maxillary: Pm, premaxillary ; V, 

 vomer; PI, palatine; J, jugal ; N, narial opening. XI. 



This species is named in honor of Miss A.M. Alexander, who 

 has not only contributed generously to the financial support of 

 the work on the vertebrates of the marine Triassic but was 

 herself the discoverer of the type specimen furnishing the largest 

 part of our information concerning the group.' 



In its fundamental outlines, the skeletal structure in Thalatto- 

 saurus is strongly suggestive of the Rhynchocephalia, but like 

 many of the so-called rhynchocephalian groups it differs so far 

 from the typical forms represented by Sphenodon, Homae- 

 osaurus, etc., that it can not be included in the same ordinal 

 division. it is likewise so different from all of the other 

 described reptilian families and orders that it must be given 

 an independent position. The family name Thalattosauridae 

 and the ordinal name Thalattosauria are therefore used to 

 express its position in the scheme of classification. 



Recently a number of groups possessing rhynchocephalian 

 characters have been tentatively brought together as orders in a 

 superorder, Diaptosauria, byOsborn.* Although diaptosaurian 

 in one sense simply spells primitive, this classification serves to 

 emphasize the distinct kinship certainly shown by many of these 



*H. F. Osborn. The Reptilian Subclasses Diapsida and Synapsida and the 

 Early History of the Diaptosauria, Mem. Am. Mus. Nat. Hist,, Vol. 1, Part 8, 1903. 



