1895.] 147 [Cope. 



angle posteriorly, as viewed from below, instead of the rounded outline 

 seen in several species. 



The form of the skull differs from that of several species where that 

 region is known. Thus in the C. burtinii, according to Van Beneden, 

 the occipital bone is broadly rounded in outline instead of triangular. In 

 C. dubium this region is triangular, but is much more elevated and less 

 produced forwards than in the G. megalophysum. It is more elevated 

 than the length from the frontal bone posteriorly, instead of being only 

 two-thirds as high as long. In the C. morenii, from Chubut, Patagonia, 

 Lydekker states that the lateral occipital crests are more elevated than 

 the apex of the occipital bone, giving a cordate outline to the posterior 

 profile. This does not occur in any known northern species. The tym- 

 panic bulla of this species is also quite different. The occipital region of 

 the G. hupscMi resembles that of the G. megalophysum more nearly than 

 that of any other species as far as knowu. In the G. capellinii Van Ben., 

 according to the descriptions and figures of Capellini, the frontal is more 

 elongate and narrower on the middle line and the tympanic bulla has not 

 the posterior median angle when viewed from below such as exists in the 

 C. megalophysum. 



Comparison with the species described by Brandt from Russia and 

 Italy, discloses numerous important differences.* The frontoparietal 

 region in the G. priscum Br. is materially shorter than in the megalophy- 

 sum. The auricular bullis of G. priscum, G. meyerii and G. kliaderii are 

 gradually acuminate to an acute apex, when viewed from the inner side, 

 and are without the convexity of the lower side and the truncation of the 

 apex characteristic of our species. The bulla of the G. rathkei is a little 

 more like that of the Chesapeake form, but it is nevertheless specifically 

 distinct. It is, when viewed from above, broadly and subequally rounded 

 at both extremities, instead of being truncate at the one and angulate at 

 the other. The extremities are of subequal width, while the anterioi 

 portion is much narrower in the G. megalophysum. 



Finally, the bulla of the G. megalophysum is of relatively larger size 

 than in any of the species noticed above. 



Measurements. 



u. 



Length of fragment below 565 



Width Of fragment 515 



Width of glenoid region from bulla 150 



Length of glenoid region from bulla (least) 100 



Width of sphenoid between foramina lacera 105 



Length of tympanic bulla below 100 



Width of tympanic bulla in front of external process 53 



Width of tympanic bulla behind external process 67 



Width at exoccipital processes .400 



* Memoires Acad. Imp. Sciences, St. Petersburg, 1873, xx, p. 143. 



