392 DR. J. E. GRAY ON STERNOTHCERUS. [Apr. 1, 



April 1, 1873. 

 Robert Hudson, Esq., F.R.S., V.P., in the Chair. 



The following papers were read : — 



1. On the Skull of Sternothcerus. By Dr. J. E. Gray, 



F.R.S. &c. 



[Eeceived February 21, 1873.] 



In my essay "On the Genera of Chehjdidce, and the characters 

 furnished by the study of their Skulls " (P. Z. S. 1864, p. 128) I was 

 unable to describe the skull of the genus Sternothcerus, as I did not 

 possess or know of the existence of any skull of the genus ; but I 

 ventured to place it in the same section as the genus Pelomedusa, 

 because its head was covered by hard, horny, symmetrical plates, and 

 because I thought I felt the zygomatic arch well developed through 

 the skin — a peculiarity that separates the African Chehjdidce from 

 the S. -American and Australian genera of this group of Tortoises, 

 and which induces me now to consider them a separate family, cha- 

 racterized by the structure of the skull, which in the African genera 

 is most completely developed, while in the Australian and S.-American 

 animals it is more or less rudimentary. 



I did not figure the skull of Pelomedusa, because it had already 

 been well figured in the Atlas of Wagler's ' Natiirl. Syst. Amphib.' 

 t. ii. figs. 36-44. This figure shows how very different the skull is 

 from that of other Hydraspidce, but does not show the base of the 

 skull, palate, and alveolar surface, which is so important as indicating 

 the food of the animal, and presents modifications that afford good 

 zoological characters. Since that period we have fortunately dis- 

 covered a very large skull, evidently belonging to the genus Ster- 

 nothcerus, which M. du Chaillu had used (as he did the new species 

 of Bush-buck which I described in the P. Z. S. 1871, p. 594) to stuff 

 out the skin of a large African mammal. 



This skull is very much larger, nearly three times as large as any 

 specimen of Sternothcerus which we have in the collection, and it 

 shows that I was right in referring this genus to the same group as 

 Pelomedusa. It has all the characters of that group more fully de- 

 veloped : that is to say, the skull is very much depressed ; the zygo- 

 matic arch is very strongly developed, being very broad and promi- 

 nent ; the middle of the upper jaw is prominent, notched on each 

 side ; and the lower jaw is very strong, with an acute produced cen- 

 tral edge fitting into a deep pit in the front of the alveolar surface 

 of the upper jaw, just within the prominent central margin. The 

 beaks covering the jaws are horny, and conform to the shape of the 

 bones, the middle of the upper part of the upper beak having a broad 

 notch for the nostrils, the beak on the side of the nose going up to 

 the upper surface of the nasal hole. 



