407 



broad bony palate, characteristic of the genus. The premaxillaries extend further back than 

 the nasals, and are relatively broader at their hinder extremities. This skull is chiefly distin- 

 guished by the superior breadth of the frontals, as compared with the preceding and larger 

 species of Marmot. The sagittal and great part of the frontal sutures are obliterated. The 

 pituitary and chiasmal fossae are distinct, though shallow. 



Presented by S. P. Pratt, Esq., F.R.S. 



2259. A mutilated cranium of another species of Arctomys, from Valparaiso. 



It is of the same size as the preceding, but differs in the minor expanse of the frontals and 

 the much smaller postorbital processes, in the bending forwards of the whole anterior root of 

 the zygoma, in the form of the thin ridge defining a deep groove on its fore part, and in 

 the greater size of the tubercle below the small antorbital foramen. The second premolar 

 and the true molar teeth are also larger in proportion in both jaws. 



Presented by S. P. Pratt, Esq., F.R.S. 



2260. A mutilated skull, indicative of a fourth species of Arctomys, from Valparaiso. 



It differs from the preceding specimen in the narrower interfrontal region, which is 

 concave transversely instead of being convex, in the longer postorbital processes, in the 

 larger relative size of the first premolar, and the smaller size, especially in the antero-poste- 

 rior diameter, of the three succeeding grinders. The ridge from the fore part of the broad 

 anterior root of the zygoma is sharp and produced, but not bent so far forwards, and the 

 groove whkh it defines is consequently shallower. The extent of the bony palate beyond the 

 last molar is more than equal to the breadth of that tooth. The premaxillaries and nasals 

 terminate behind on the same transverse line. The angle of the jaw is singularly bent out- 

 wards at its extremity and bent inwards at its lower border. The enamel of the incisors is 

 white : in the two preceding and similarly sized specimens it is deep orange. 



Presented by S. P. Pratt, Esq., F.R.S. 



Genus Spermophilus. 



2261. The skeleton of the Souslik, or Siberian Marmot (Spermophilus ffuttatus). 



So far as the vertebral formula can be shown, there are 7 cervical, 12 dorsal, and / lumbar : 

 the sacral and caudal series are incomplete from injury. 



Presented by Sir Anthony Carlisle, F.R.S. 



2262. The skull of the Variegated Marmot (Spermophilus undulatus). 



In this, as in the preceding species, the upper contour of the cranium is more convex than 

 in the true Marmot. The squamous perforation is much reduced, and partly concealed by 

 the hinder root of the zygoma. It is larger and more posterior in position in the Spermo- 

 philus guttatus. The frontals are relatively broader, and the nasals narrower in the present 

 species. 



Hunterian. 



