530 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



parietals, as it is usually, if not always, found in the reptilia. The 

 median superior border of the supraoccipital is not united by suture 

 with the overlying parietals, but presents a finished grooved border 

 for cartilagenous attachment — a condition foimd in many of the 

 Predentate dinosauria. 



The presence of such a border casts grave doubt on the authenticity 

 of Huene's determination, where he depicts ^ the supraoccipital as 

 attached by jagged suture with a dermosupraoccipital that is inter- 

 posed between it and the parietals. Either the upper mecUan portion 

 of these coalesced occipital bones in No. 8635, U.S.N.M. (fig. 1) 

 represent the dermosupraoccipital or else Huene's interpretation is 

 in error. All the evidence sustains the latter conclusion, but as to 

 how the dermosupraoccipital does articulate with the parietals the 

 present specimen offers no evidence. 



The complete, uncrushed left squamosal is present, and it appears 

 to clear up some of the earUer determinations of authors. The upper 

 end is obliquely truncated, presenting on the superior surface of the 

 upper end an articular face, the outer half of which is certainly for 

 articulation with the posterior branch of the postorbital; the inner 

 half of this facet meets the outer end of the parietal. It should be 

 stated, however, that the parietal was found detached, but everything 

 about it appeared to indicate a close union with the posterior branch 

 of the postorbital and squamosal as shown in figure 1. 



There was no evidence of the separation of the posterior extremities 

 of these bones by an interposed supratemporal bone such as found 

 by Huene, and I think it highly improbable that such a condition 

 existed, for were the supratemporal present in this position in Dime- 

 trodon, contact between the parietal and squamosal would be severed — 

 a most unusual condition in the reptiUa. 



Broom m liis restoration ' of the skull of Dimetrodon shows the parie- 

 tal and postorbital in close apposition and both properly in contact 

 with the squamosal. In view of the evidence now before me I can 

 see no possibility of there being an element thrust in between the 

 posterior extremities of these bones such as found by von Huene. 



The quadratojugal is another bone whose limitations are not as 

 yet fuUy and satisfactorily determined. This bone is represented in 

 the present skull by the greater portion of the left element. It had 

 not been identified at the time of articulating the skull, so does not 

 appear in the illustrations. As preserved it is a small irregularly 

 shaped bone, with a short lateral process which extended forward to 

 overlap the posterior end of the jugal (see fig. 1, qj.) and a superior 

 process which extended upward behind the quadrate to unite with the 

 squamosal as shown in figure 1. Huene has correctly viewed the 

 lateral extent of the quadratojugal (fig. 42, p. 357), but he appears 

 to have been in error regarding its superior process, which he con- 



> Bull. Amer. Mus. Nat. Hist., vol. 32, 1913, p. 359, fig. 44 A 



* Broom, R. Bull. Amer. Mus. Nat. Hist., vol. 28, 1910, p. 225, fig. 19. 



