4 MR, G. A. BOULENGER ON CHELONIAN REMAINS. [Jan. 6, 



2. On some Chelonian Remains preserved in the Museum of 

 the Royal College of Surgeons. By G. A. Boulenger. 



[Eeceived December 8, 1890.] 



In the course of a recent examination of the osteological material 

 preserved in the Museum of the Royal College of Surgeons, I have 

 come across a few interesting specimens of extinct and fossil Che- 

 lonians, hitherto overlooked or wrongly interpreted, which Professor 

 Stewart has most kindly placed at my disposal for description. 



1. On the Skull of an extinct Land-Tortoise, probably from 

 Mauritius, indicating a new Species (Testudo microtympanum). 



A skull without mandible, from the Hunterian Collection (no. 

 1058), differs considerably from that of any of the gigantic Land- 

 Tortoises hitherto described. As it comes nearest to Testudo tri- 

 serrata, Gthr. ^, an extinct form from Mauritius, we may assume, in 

 the absence of any information as to its origin, that it probably 

 came from that or some neighbouring island. T. triserrata is the 

 only species of Testudo known to possess two median ridges on the 

 alveolar surface of the maxillary, and this character is shown on the 

 skull for which the name T. microtympanum is proposed, in allusion 

 to the very small tympanic cavity, which is one of its principal 

 distinctive features. Another important distinction is to be found 

 in the great backward prolongation of the palatines and vomers, 

 the latter bone forming a suture with the basisphenoid. 



The following is a description of this interesting skull : — 



millim. 



Total length to extremity of occipital crest .... 135 



Length to extremity of occipital condyle 102 



Greatest width 98 



Diameter of orbit 33 



Interorbital width 45 



Greatest diameter of tympanum 21 



Frontal region convex ; interorbital width greater than diameter 

 of orbit ; praefronto-frontal suture oblique, extending beyond the 

 middle of the upper border of the orbit ; suture between the prse- 

 frontals not quite half as long as that between the frontals ; only 

 the anterior half of the parietals forms a flat surface, and the 

 sagittal suture is all but obliterated. Postorbital arch rather 

 slender, narrower than the zygomatic, which is formed by the post- 

 frontal, the jugal, and the quadratojugal ; postfrontal in contact with 

 quadratojugal. Tympanum small, its greatest (vertical) diameter 

 only about two-thirds the diameter of the orbit. Maxillary with 



' A. Giinther, 'The Gigantic Land-Tortoises (Living and Extinct) in the 

 Collection of the British Museum ' (1877), p. 44, pi. xxii. fig. A. 



