PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 39 



The skull of Ophiacodon * is remarkable among Permian vertebrates for its 

 relatively large size and delicacy of structure. In part the result, perhaps, of the 

 extreme thinness of most of its bones, the skull was more or less compressed from 

 side to side in fossilization, though without affecting its general shape and con- 

 tours. So frail is its structure that it was found inexpedient to remove it entirely 

 from its supporting matrix. It was, therefore, carefully cleaned of its investing 

 matrix on its upper or right side and embedded in a plaster mold, after which it 

 was turned over, with the rest of the skeleton, and cleaned on the other, the better- 

 preserved side. Both sides have been photographed and studied by us, but the 

 right side is no longer accessible, embedded as it is in plaster for the better preser- 

 vation of the specimen. 



The skull is remarkably narrow, high, and long. The very small nares are at 

 the extreme front end; the small orbits are far posterior. The upper side is flat- 

 tened in the frontal and parietal region; its greatest width is just back of the orbits. 

 The occipital region forms a declivity, as in Dimetrodon. The parietal foramen has 

 not been detected with certainty ; it must have been small. Immediately in front 



Fig. 23. — Ophiacodon mirus Marsh. Lateral view of skull, X }j. 

 pa, parietal; ^0, postorbital ; pf, prefrontal; I, lachrymal; j, 

 jugal; qi, quadrato-jugal ; g, quadrate. 



of the orbits the upper surface narrows ; thence to the nares the border, formed 

 chiefly by the nasals, is gently convex in outline. Doubtless in life the very broad 

 sides of the face were gently convex, but, as preserved, the thin bones forming 

 them are nearly in contact, producing a light concavity between the thickened 

 alveolar border of the maxilla and the thickened nasal border; the bones of this 

 region are scarcely thicker than writing paper, for the most part, and are so cracked 

 as to render impossible the certain determination of their connecting sutures. 



In fig. 23 the skull is shown as it lies in its matrix, except that the two posterior 

 premaxillary teeth have been brought into anatomical association with the first 

 one. The general shape of the skull, as shown, seems to be quite that of life; pos- 

 sibly the dentigerous margin of the maxilla is a trifle too convex in outline. The 

 nares, as has been said, are very small, and are situated near the extreme front 

 end of the skull. The orifice of each naris is nearly circular in outHne, directed 

 laterally and perhaps a little forward in life. The orbits also are remarkably small 

 in comparison with the size of the skull. They are subtriangular in shape, broader 

 above, the lower end separated from the posterior end of the maxillae by the mod- 



* Ophiacodon mirus Marsh, American Journal of Science, xv, 411, May 1878; Baur and Case, Trans. 

 Amer. Phil. Soc, n.s., 1899, p. 5, 1907; Williston, American Permian Vertebrates, p. 81, plates xxxiv- 

 XXXVII, Oct. 191 1. 



