REPTILIA : PLATYHYSTRIX 135 



GENUS INCERTAE SEDIS 

 PLATYHYSTRIX 

 Williston, Sdence, XXXIII, 631, 1911. 



Platyhystrix rugosus. Plates XXXVI, XXXVII. 



Ctenosaurus rugosus Case, Bull. Amer. Mus. Nat. Hist., XXVIII, 1910. 

 ? Zatrachys apicalis Cope, Amer. Nat., XV, 1020, December, 1881. 



This species was based by Case on a few neural spines of remark- 

 able character,, some of which had been associated by Cope with 

 his type specimen of Zatrachys apicalis, evidently the ones which 

 he describes as "narrow flat bones, which I suppose to be neural 

 spines, which are ornamented with inosculating ridges." The 

 species was referred provisionally by Case to the genus Ctenosaurus 

 Huene, from the European Trias. The essential part of Case's 

 description is as follows: 



"The spines here described are not very long, the base is nar- 

 rowed with almost equal antero-posterior and transverse diameters. 

 The upper portion becomes thinner, and is elongated in the antero- 

 posterior diameter. The sides of the spines, from the base to the 

 top, are covered with small irregidar bosses similar to those on the 

 skull of many amphibians. Some of the spines are more slender 

 and less expanded antero-posteriorly at the top than others, but 

 all have the characteristic sculpture. Fragments of scapulae and 

 limb bones associated with the spines are typically pelycosaurian 

 in form." 



In the Yale collections of the Arroya boiie-bed of New Mexico 

 are several spines which I must identify specifically with those 

 described by Case, though none agrees precisely with his descrip- 

 tion. One of these is shown in Plate XXVI, Fig. i, two-thirds 

 natural size. It is nearly complete; some of the fragments from 

 near the lower end had crumbled so that actual contact could not 

 be made, and it is possible that the interval I have left may be 

 slightly too great or too small. The centrum immediately asso- 

 ciated with the spine in all probability belongs with it, though 



