MORPHOLOGICAL REVISION 67 



MORPHOLOGICAL REVISION. 



Genus DIADECTES Cope. (Plates 1-9, 14.) 



Characteristic specimens: No. 4684 Am. Mus. Nat. Hist.; a nearly complete 

 skeleton lacking skull and foot bones. No. 4839 Am. Mus. Nat. Hist.; a nearly 

 perfect skull. No. 1075 University of Chicago; a nearly complete skeleton, lacking 

 only the feet. 



Nos. 4684 and 4839 have been identified as D. phaseolinus. No. 1075 can not 

 be specifically identified, but it belongs very close to the above specimens, though 

 smaller. In the following description, which may be taken as that of Diadectes 

 phaseolinus, the details are largely taken from the two specimens in the American 

 Museum, as the Chicago specimen has not been cleaned or mounted. 



The skull of the genus is represented by numerous more or less complete 

 specimens, but none show the internal structure at all well except No. 4839. This 

 is very perfect, lacking only the premaxillary and the articular portion of the quadrate 

 of the left side. The form of the skull is quite similar to that of Pareiasaurus. 

 The posterior end is much wider than the anterior, the sides slope outward and 

 downward, so that the upper surface is nar- 

 rower than the lower; the distance across the 

 top of the skull in the parietal region is not 

 more than half of that across the articular ends 

 of the quadrate bones. The posterior face 

 falls off almost vertically. The top is flat and 

 descends slightly from the posterior to the an- 

 terior end. 



In most specimens the surface of the skull 

 is covered by a rough sculpture which dimin- 

 ishes anteriorly, but is renewed on the premax- 

 illaries in a series of roughly parallel grooves. 

 The bones are so closely united that the su- 

 tures can not be traced on the upper surface. 

 One specimen in the American Museum shows _ 



the top of a skull with the cast of the lower F10.19. — Fragmect of the top of tlie «kuU of Difl<&«« 



surface; on this cast and on the lower surface »p-. »howmg suture.. x4. No. 4845 Am. Mus. 

 of the bones the course of the sutures can be traced. The parietals are large 

 plates surrounding the parietal foramen and reaching to the posterior edge of the 

 skull. The supraoccipital and other (indeterminable) bones form the posterior 

 surface. The large squamosal bones articulate with the parietal, postorbital, and 

 jugal; there is no evidence of the presence of a tabulare. Just anterior to the parietal 

 foramen the suture between the parietal and frontal runs nearly straight across the 

 top of the skull and meets the postfrontal on either side. The frontal is kept from 

 taking part in the orbits by the union of the prefrontal and postfrontal. 



The parietal foramen is "enormous," as described by Cope. Near the posterior 

 edge of the skull there are deep pits, one on each side, approximately in the line 

 of the suture between the parietal and squamosal. From a study of less perfect 

 specimens these have been reported as probable rudimentary openings, but in 

 these specimens they are certainly closed at the bottom. This character seems to 

 have been extremely variable, recalling the condition in the Pelycosauria where the 

 supratemporal opening may be persistent or may be closed. 



Posterior aspect: The occipital condyle is wider than long and is excavated on 

 the upper border by the foramen magnum, so that it presents a broad heart-shaped 



