61 



louring there are also points of distinction : in lieu of the dull brown 

 tint on the top of the head and back, the present species possesses 

 rich rufous brown feathers. In one specimen the body is yellowish 

 white beneath, but in the other it is pure white. 



Mr. Waterhouse then proceeded to make some observations upon 

 a series of skulls of Rodents which were upon the table. These 

 skulls belonged chiefly to species of the various genera contained in 

 the families ChinchillideR (consisting of the genera Chinchilla, Lagotis, 

 and Lagostomus), and Caviida — composed of the genera Cavia, Ke- 

 rodon, Dolichotis, and Hydrochcerus. Numerous points of resem- 

 blance between these two families were dwelt upon, more particu- 

 larly in the structure of the teeth, the form of the palate, the con- 

 tracted glenoid cavity, the form of the lower jaw, and direction of 

 the lower pair of incisors. The Caviida, however, possess certain 

 characters, independent of those observable in the form of the teeth, 

 which renders it easy to distinguish them from the Chinchillidce. He 

 alluded especially to the shortness of the condyloid process of the 

 lower jaw, the forward position of the coronoid process, the peculiar 

 projecting ridge on the outer side of the horizontal ramus, and the 

 form of the descending ramus or angle of the jaw ; this projects con- 

 siderably beyond the Hne of the coronoid process, whereas in the 

 Chinchillida it terminates in a line with the posterior portion of the 

 coronoid process, or projects but slightly beyond that line. 



Among the Chinchillida, the Lagostomus trichodactylus, observes 

 Mr. Waterhouse, approaches most nearly to the Cavies, the angle 

 of the lower jaw being less acute and the coronoid process more for- 

 ward than in the other species. 



In the imperfect state of the palate, the narrowness of the ante- 

 rior and posterior sphenoids, the form of the occipital condyles, the 

 form of the articular portion of the lower jaw, and the almost hori- 

 zontal direction of the incisors of the lower jaw of the Chinchillas 

 and Cavies, Mr. Waterhouse stated he had found characters which 

 induced him to place those animals next before the Leporidce. 



