Zoological Society. 429 



the last-mentioned colour prevails on the sides of the body, where 

 numerous long interspersed white hairs are observable, as well as on 

 the rump. The under parts of the body are of a cream-yellow. The 

 ears are rather large, deeply emarginated behind, and clothed inter- 

 nally with small pale hairs, excepting towards the margin, where they 

 assume a dusky hue ; externally the ears are furnished with minute 

 dusky hairs, but at the base they are white. The head, in the region 

 of the ear, is very pale ; the throat, inner side of the legs ana the 

 tarsi are white ; the tail is about equal to the body in length ; the 

 basal half is tolerably well clothed with short hairs, which are black 

 on the upper surface and dirty white on the under ; on the apical 

 half the hairs are longer (averaging rather more than a quarter of an 

 inch in length) and almost entirely black. The fur is long and mo- 

 derately soft. 



The Octodon Bridgesii differs from the O. Cumingii (or 0. Degus, 

 as it should be called) in being considerably larger, of a less bright 

 colour, and in having the tail longer and less distinctly tufted at the 

 apex ; the feet moreover are white, or very nearly so. 



The dimensions given are taken from two specimens, one in the 

 British Museum collection and the other in that of the Zoological 

 Societjr, which were brought to this country by Thomas Bridges, 

 Esq., a very zealous collector and good observer, after whom I have 

 named the species. The skulls of these two specimens agree with 

 each other, and differ considerably from those of the 0. Cumingii. 

 In the first place they are about one-third larger, less arched above ; 

 the nasal bones are narrower in proportion, the frontal bones smaller 

 and more contracted in front, and the palate is also more contracted 

 in front. The molar teeth of the upper jaw have the inner fold of 

 enamel deeper. In the lower jaw the molar teeth have the lateral 

 angles more produced, and their transverse diameter is consequently 

 greater in proportion. The coronoid process is distinctly larger in 

 proportion. Other differences of size and proportion will be per- 

 ceived upon comparing the following dimensions : — 



0. Cumingii. 0. Bridgesii. 



in. lin. in. lin. 



Total length of cranium 1 6| 1 9|- 



Greatest width 10| 1 0^ 



Length of nasal bones 7 8^ 



Length of frontal bones 6 J 6% 



Width of interorbital space 5 4 J 



Total length of zygomatic arch 8j 11 



Length from front of superior incisors to the 1 ^ - j 6* 



molar teeth J ^ ^ 



Length of the four molar teeth taken together 4J 5^ 



Width of incisor teeth of upper jaw 1^ IJ 



Width of palate between foremost molars . . l^J ^ ^ 



Width of palate between hinder molars .... 2 ^ 2§ 



Length of ramus of lower jaw ^ ^ ^3 ^ ^| 



Height of ditto in a vertical line, dropped! q r^ q ^ 



from the condyle / ^ 



