24 NEW REPTILES AND STEGOCEPHALIANS FROM 



openings are the same as in No. 7469 and there is the same meeting of two distinct 

 bones at the posterior edge and the same distinct articular element. 



Eight interclavicles were found in the same region as the skull of Bueltneria. Five 

 of these are nearly complete; three are accompanied by more or less complete clavicles; 

 three are represented by the posterior portion only. These bones are shown in figure 5, 

 and plates 2 c, 3, and 4. It is evident that none of these forms is specifically identical 

 with any of the described forms from the Upper Triassic of Europe, and it is probable 

 that the difference is of generic value. Figure 6, copied from Fraas, 1 shows the char- 

 acteristic form of the interclavicles in Metoposaurus, Cyclotosaurus, and Mastodonsaurus. 

 In comparing these with the interclavicles from the Texas Triassic, it is evident that 

 there is a great difference in the proportions; in the American forms the posterior pro- 

 longation is much less in relation to the anterior. In the specimen previously described 

 as Metoposaurus jonesi, No. 3814 of the University of Michigan collection, the form 

 most closely approaches that figured by Fraas as Metoposaurus in the shortness of the 

 anterior process and the breadth as compared with the length, but the posterior process 

 is much sharper and the sculpture is very different. In all of Fraas's figures there is 

 shown a strong posterior prolongation of the clavicles in the region of the articulation 

 with the shoulder girdle, which is apparently absent in the Texas forms, though this is 

 not absolutely certain, as all of the clavicles, except No. 3814, are imperfect in this 

 region. 



C 



Fio. 6. Outlines of interclavicles and clavicles. 



A. Metoposaurus, after Fraas. B. Cydotosaurus, after Fraas. C. Mastodonsaurus, 



after Fraas. 



The figures showing the outline of the interclavicles have all been reduced to the 

 same scale on the single line which is comparable in all of the specimens, i. e., the 

 breadth just at the posterior edge of the articular faces for the clavicles. The dis- 

 proportion between the breadth of the interclavicles and the length of the posterior 

 process posterior to this line is sufficiently striking in the different specimens to need no 

 comment. Working out the proportion between these lines in all of the specimens 

 results in an almost perfect series, with no break where a line can be drawn between 

 groups. The varying outlines warrant the belief that there are several distinct species, 

 but upon such incomplete material the author does not feel that new genera or even 

 species should be founded. Future discoveries will undoubtedly associate the different 

 interclavicles with more characteristic parts of the skeleton; and if the differences in 

 outline and proportions are shown to be more than developmental or individual vari- 

 ations, new names may be based on such characters. 



1 Fraas, E., Neue Labyrinthodonten aus der Scliwabischcn Trias, Paleontographica, Bd. i.x, p. 286, 1913. 



