LACEETILIA. 779 



Platyrhachis unipedalis Cope. 



JHacium unipeddle Cope. Synopsis of New Vertebrata of Colorado, 1873, p. 18. Cremastoeaurug unipe- 

 dalis Cope. Annual Report U. S. Geol. Surv. Terrs., 1873 (1874), p. 516. 



Plate LX; fig. 19. 



Represented by a sacral vertebra of an individual much larger than 

 any of those of the last-described species, and a little smaller than those of 

 the species next following, characterized by the unusual protuberance of the 

 articular ball and absence of flattening of the centrum below. Centrum 

 depressed ; plane longitudinally convex in transverse section. An annular 

 groove round the ball. Diapophysis elongate, slightly depressed. 



Measurements. 



M. 

 Length of centrum 0.0034 



Diameter of cup ^t™"^^^'"^^ ■ 00=^" 



i vertical 0018 



Were this vertebra part of an individual of the P. rhamhastes, its articu- 

 lar faces would have been more rather than less depressed than the dorsal 

 vertebrae which represent it. 



From Horse .Tail Creek, Northeastern Colorado. 



Platyrhachis rhambastes Cope. 



Plate LX ; fig. 18. 



Established on seven dorsal vertebrae, which I formerly regarded as 

 belonging to the Cremastosaurus carinicollis. (Annual Report U. S. Greol. 

 Surv. Terrs., 1873 (1874), p. 515. They differ very much from the 

 cervical vertebrae on which the latter genus is based ; too much, I believe, 

 to render it probable that they belong to lizards of the same genus. Tliis 

 also in spite of the fact that the difference is someAvhat like that which pre- 

 vails between cervical and dorsal vertebrae of many genera of Lacertilia. 

 The inferior carina in the Cremastosaurus is not a hypapophysis of tlie usual 

 kind found on only a few of the cervicals, but continues undiminished to 

 the sixth and last I possess of the series. The articular ball at this point 

 shows no indication of the depression characteristic of the dorsals, and 

 which is usual at this point, even in species where the anterior cervicals 

 have subround articular extremities. 



