190 MEMOIRS OF THE CARNEGIE MUSEUM 



so very slight and faintly marked; and a large pneumatic foramen is seen upon its 

 outer side a very unusual place for this aperture. 



Its mandibular foot is narrow antero-posteriorly and very wide transversely. 

 Two facets occupy its lower surface, separated from each other by a concave notch 

 which is deepest anteriorly. 



The bone also presents a smooth articular surface for the quadrato-jugal at the 

 point above mentioned, while a large convex facet is offered to the pterygoidal cup 

 of the pterygoid of the corresponding side. 



We find the external openings to the ear to be very small, and hid from sight 

 upon direct lateral view by the quadrate. A sphenotic process is well developed, 

 but the mastoidal one is simply a roughened line ; between the two is a wide crota- 

 phyte valley leading from the fossa of the same name, which is here small, incon- 

 spicuous, and entirely lateral. 



The orbital cavity itself is thus seen to be deep and capacious, lacking bony walls 

 principally upon its inferior and anterior aspects. They are more complete in P. 

 sharpei (PI. XXVII., Fig. 37). 



Upon its under side this skull presents a number of points of interest. The 

 anterior moiety of the superior mandible is here seen to be longitudinally grooved 

 by a broad and shallow furrow, which gradually becomes somewhat narrower as we 

 proceed backward, to finally merge into the convex, median portion of the hinder 

 half of this great rostrum. Along its median line it is marked by a few scattered, 

 slit-like foramina that lead into its shallow interior, which latter is largely filled with 

 an open mass of spongy, osseous tissue, continuous with the maxillo-palatines behind. 



The palatine bodies, including their heads, fuse together for their entire extent 

 in the median plane. Resulting from this union we have a single, descending, 

 median carination, composed of the united inner keels of the palatine bodies and a 

 similar superior median one composed of the ascending processes of the same. 



The latter is truncated just before reaching the maxillo-palatine bodies. 



This skull lacks basi-pterygoid processes, while the pterygoids themselves are 

 short, thick set bones, with large anterior and posterior heads, and sharpened longi- 

 tudinal crests on the superior aspects of their shafts. 



The basi-temporal triangle is small and its area concave. A thin, pointed lip of 

 bone eaves over the entrance to the Eustachian tubes, which are here apparently 

 thoroughly surrounded by bony walls. 



We find the foramen magnum situated at the bottom of a broad, deep, and 

 transverse concavity. This excavation is bounded on either side by the dome-like 

 mastoid prominences, in front by the line of the base of the basi-temporal triangle, 



