365 



slender than in the Guinea Pig. The auditory bulla is pierced at the base of the external 

 meatus : it has been laid open on the left side, showing the cells extending into the elevated 

 mastoid. The lacrymal bone is very small and imperforate. 



Purchased. 



Genus Lagostomus. 



2009. The right humerus of the Viscachia (Lagostomus trichodactylus). 



It is not perforated either between the condyles or above the inner condyle. It is thick in 

 proportion to its length, and is characterized by a well-defined deltoid process projecting 

 above the middle of the shaft. 



Presented by Hugh Cuming, Esq., F.L.S. 



2010. The left humerus of the same Viscachia, in longitudinal section. 



Presented by Hugh Cuming, Esq., F.L.S. 



2011. The middle and terminal phalanges of one of the toes of the Viscachia, with 

 the claw ; which is strong, sharp-pointed, almost straight, and grooved at its 

 under part. Presented by Hugh Cuming, Esq., F.L.S. 



Genus Ctenomys. 



Dental formula : t |=T, p j, i=5= 20 - 



> 



2012. A mutilated skull of the Magellanic Ctenomys (Ctenomys Magellanicus). 



It is remarkable for the enormous expanse of the auditory bullse, which extend from the 

 part of the mastoid inclosed between the parietal, superoccipital and squamosal, downwards 

 and forwards to the pterygoids. The exoccipital sends outwards a long narrow process, which 

 arches over the bulla to articulate with the squamosal and tympanic, and the paroccipital 

 stretches outwards and expands into a broad thin plate of bone, which supports the lower 

 and posterior prominence of the bulla. The vacuity in the side of the cranial walls is left 

 between the base of the clamping process of the squamosal and the tympanic. There is a 

 small transversely oblong interparietal. The sagittal and frontal sutures are retained, and 

 the temporal ridges are divided by a broad, smooth, almost flattened tract of the frontal and 

 parietal. The premaxillaries are united by short and deeply-indented sutures with the 

 frontals, the teeth of which extend beyond the nasals. The malar bone is three-sided, with 

 a strong external ridge. A well-marked antorbital process accompanies the upper and ante- 

 rior root of the zygoma. The antorbital vacuity is of considerable size. The molars are four 

 in number on each side of both jaws, rootless, strongly curved : the last, m 3, is very small. 



Presented by Captain King, R.N. 



