DINOM VID4E—CAVUDA 489 
Celogenys.i—tThis genus is readily characterised by the presence 
of five hind toes, and the extraordinary development of its zygo- 
matic arches, which are enormously expanded vertically, forming 
great convex bony capsules on the sides of the face, enclosing 
on each side a large cavity lined with mucous membrane, and 
communicating by a small opening with the mouth. The Paca 
C. paca) is about 2 feet long, and, like the species of Dasyprocta, lives 
generally in the forests or along the banks of rivers. This species 
appears to date from the epoch of the Pleistocene deposits of the 
Brazilian caves. A smaller species from Ecuador, living at ele- 
vations of from 6000 to 10,000 feet, has been described as 
C. taczunowskti. 
Family DINOMYIDA. 
Distinguished from the Dasyproctide by the cleft upper lip, 
rather long and bushy tail, the presence of four digits in both fore 
and hind feet, and the complete clavicles. The manubrium is 
broad ; the optic foramina are confluent; the incisors broad ; and 
the molars rootless, with enamel-folds dividing them into transverse 
lamine. 
Dinonys.2—The sole representative of this family is the Rodent 
known as D. branicki, of which hitherto only a single specimen has 
been obtained. This was captured in Peru, where it was found at 
daybreak walking about a courtyard; the inhabitants of the dis- 
trict were previously unacquainted with the species, from which 
its extreme rarity may be inferred. Externally it resembles much 
the Paca, having similar S-like nostrils; but in the laminated 
molars, and many features of the skeleton, it differs from all the 
other Rodents with hoof-like nails. It is regarded by its describer, 
the late Professor Peters, as a connecting link between the 
Octodontide, Chinchillide, Dasyproctide, and Caviide. 
Family CAVUD®. 
Terrestrial or natatorial forms, with short incisors, strong man- 
dibular masseteric ridges, long and curved paroccipitals, and palate 
contracted in front. Fore feet with four digits, hind feet with 
three. Clavicles imperfect. Molars divided by enamel-folds into 
transverse laminz ; milk-teeth shed before birth. Other characters 
as in Dasyproctide. Neotropical region. 
Cavia.3—Limbs and ears short, subequal ; tail none. Vertebre : 
C7,D13,L6,84,C7. This genus includes several species widely 
1 F. Cuvier, Ann. du Afuséwm, vol. x. p. 208 (1807). 
* Peters, Monatsber, Ak. Berlin, 1873, p. 551. 
3 Pallas, Mise. Zool. p. 80 (1766) ; ex Klein. 
