60 MR. E. T. BENNETT ON THE CHINCHILLID#, 
Lacostomus tricHopactyLus, Brookes, in Linn. Trans., xvi. p. 102. t. 9. (animal 
et ejus sceleton.)—Less., Ill. Zool., livr. 3. pl. 8.—Goldf., Naturh. Atlas, 
Th. III. p. 262. t. 289. f. 2. (tigg. Brookes.) 
Dipus maximus, Blainv.— Desm., in Nouv. Dict. Hist. Nat., xiii. p. 117.— 
F. Cuv., in Dict. Sci. Nat., xviii. p. 471. 
Marmot Diana, Griff., Transl. An. Kingd., iii. p. 170. ©. fig. 
Callomys Viscaccia, Isid. Geoff., in Ann. Sci. Nat., xxi. p. 291, 
Querendum adhuc est ubi referendum 
Callomys aureus, Isid. Geoff., in Ann. Sci. Nat., xxi. p. 291. 
An generis Chinchillze ? 
The Herbivorous subdivision of Rodentia, as proposed by M. Fréderic Cuvier, em- 
braces several strongly marked groups of forms, having an immediate affinity with each 
other, although it must be confessed that several of them are also nearly related to 
genera of the Omnivorous tribe. The persistence of the pulp of their molar teeth, and 
the consequent unceasing growth of those teeth, indicate, however, an inferior degree 
of development as regards those most essential organs ; and appear to me to offer a 
sufficient bond of connexion between them. 
Of the families composing this tribe, the Leporide, including Lepus and Lagomys, 
and represented by the Hares and Rabbits, are characterized by their supplemental in- 
cisors, and by the tendency to still further subdivision in the anterior pair, which in 
Lagomys especially are so deeply grooved and have the two portions so different in size 
and form, as to simulate two distinct teeth on each side of the symphysis of the upper 
jaw. The molar teeth are not in these animals opposed crown to crown, but those of 
the lower jaw pass, when the mouth is closed, almost entirely within those of the upper, 
and a considerable degree of lateral motion is consequently requisite for the due masti- 
cation of the food; which motion is much facilitated by the almost hemispherical form 
of the condyles of the lower jaw, and the freedom of their articulation in small glenoid 
cavities. By means of this organization the surfaces of the molar teeth are unequally 
worn, and offer transverse projecting lines of enamel, with intermediate depressions of 
the osseous substance. 
To this family the Chinchillide are evidently very nearly related, in the lamellated 
composition of their molar teeth ; in the general form of the body; in the nature of 
the hairy covering; and in habits and mode of life. They differ, however, in many 
essential particulars, such as the simplicity of their incisor, and the reduced number of 
their molar, teeth; the elongated form of the condyles of the lower jaw, and the con- 
sequent limitation of the process of mastication to a motion forwards and backwards, 
wearing down the crowns of the molars (which are exactly opposed to each other) in 
a perfectly equal manner; the depression of the upper surface of the head, which in 
the Hares and Rabbits is very strongly arched throughout its whole extent; the deep 
