The list is completed by Aepyprymnus rufescens, which differs from all the others by the hairy muzzle, and the absence of inflation in the auditory bullae and of vacuities in the palate.
The family, Chinchillidae, typified by the wellknown chinchilla, includes a small number of South American rodents with large ears and proportionately great auditory bullae in the skull, elongated hind-limbs, bushy tails, very soft fur and perfect clavicles.
Comparatively few examples of golden bullae have survived.
In the members of the typical genus Potorous (formerly known as Hypsiprymnus) the head is long and slender, with the auditory bullae somewhat swollen; while the ridges on the first two premolars are few and perpendicular, and there are large vacuities on the palate.
The tail and ears are generally very long; while, in correlation with the size of the latter, the auditory bullae of the skull are also large.
In Chinchilla the fore-feet have five and the hind four digits, the tail is long and bushy, and the auditory bullae are enormous, appearing on the top of the skull; Lagidium has four digits in both foreand hind-feet, and Lagostomus three only in the hindfeet, while the auditory bullae are much smaller (see Chinchilla and Viscacha).
Even in the north, metal bullae were also occasionally in use.
As is always the case with large-eared animals, the tympanic bullae of the skull are of unusually large size; the size varying in the different genera according to that of the ears.
On special occasions golden bullae were issued by the Byzantine emperors, by the popes, FIG.
The sovereigns of Spain, too, made use of the same material; and in the Byzantine empire leaden bullae seem to have been universally employed, not only by emperors and state officials but also by private persons.