CACOPS ASPIDEPHORUS 253 



CaCOPS ASPIDEPHORUS — GeNUS AND SpECIES NEW 



SKULL 

 (Plates 6, 7, 8) 



Two skulls, nearly complete, and portions of two others have so far 

 been recovered from the matrix. Of these the one in the mounted skele- 

 ton was quite complete, but suffered slightly at the front extremity in 

 its collection. The best specimen, however, the one from which the fol- 

 lowing description has been drawn, was a skull quite complete, attached 

 to another skeleton, from which the posterior end of the mandibles only 

 was lost in collecting. This skull is slightly smaller than the moiinted 

 one and had suffered very little distortion. It has been freed from every 

 particle of matrix, even that of the brain and nasal cavities. Unfortu- 

 nately, in none of the specimens has it been possible to determine the 

 sutures, in part because of the complete ossification of the bones ; in part, 

 perhaps, because the removal of the thin investing matrix has obliterated 

 whatever indications of them might have been present. The dermal 

 surface is everywhere rugose, with small, irregular pits and ridges. 



The skull is broad and depressed, broadest opposite the posterior part 

 of the orbits, with a gentle, perhaps somewhat irregular, convexity on the 

 sides. The epiotics project backward strongly, leaving a deep concavity 

 in the middle behind. The nares are large, oval in outline, directed up- 

 ward, forward, and outward, broadly separated in the middle, and ap- 

 proaching closely the margin of the maxillae. The orbits are large, sub- 

 circular in outline, the opening looking obliquely upward. Near the 

 middle of their front margin the border is angularly thickened, descend- 

 ing in a steep declivity outwardly. In the middle posteriorly, also, there 

 is a similar, but more angular, thickening, which extends back as a ridge 

 to form the lateral margin of the cranial table, overhanging the otic cav- 

 ity posteriorly. Almost continuous with the upper orbital margin, there 

 is another elevated ridge running backward and outward to join the lat- 

 eral border over the middle of the otic cavity. Between these two ridges; 

 there is a triangular space of considerable size, more or less depressed in 

 its middle. The least distance between the orbits, near their middle, is 

 but little or no more than one-half the lateral diameter of the orbit. The 

 large parietal opening is located about one-third of the distance between 

 the hind borders of the orbits and the occipital margin in the middle. 

 Just in front of the concave hind border of the table the margin is ele- 

 vated into a prominent rugose crest or ridge, highest in the middle, possi- 

 bly for the attachment of nuchal muscles. The cranial table in front of 



XVIII — BUI.L. Geol.: Soc, Am., Vol. 21, ino9 



