The DASYPROCTIDÆ have but few fossil representatives, and the undoubted ones are all from the bone-caves of Brazil, which furnished Dr. Lund with two Agoutis and two Pacas. Of the former, one is described as _Dasyprocta capreolus_; the second is allied to the living _D. caudata_. The two species of _Cœlogenys_ are extinct. Some teeth, found in Tertiary deposits of the Puy-de-Dôme, have been referred to _Dasyprocta_, but this determination is excessively doubtful. _Diobroticus schmerlingi_ from Belgian caves has been placed with the Castoridæ. Of the CAVIIDÆ, Dr. Lund obtained three species of the genus _Cavia_, and two of _Hydrochœrus_, from Brazilian bone-caves. Of the latter, one was allied to the existing Capybara; the other was a gigantic species, measuring about five feet in length. Dr. Leidy has described a species (_Hydrochœrus æsopi_) from teeth found in Post-Pliocene deposits in South Carolina; and the Pampean deposits of the same age furnished M. D’Orbigny with the remains of a Cavy (_Cavia antiqua_) which, however, is doubtfully distinct from the Patagonian species. The remains of species of the family LEPORIDÆ are very abundant in some Post-Pliocene cave deposits on both sides of the Atlantic, and in several cases the species are evidently identical with those now living. Besides these, species of the genus _Lepus_ have been found in Pliocene and Miocene beds in France. In North America three extinct Leporine genera have been recognised, differing from _Lepus_ in certain peculiarities of the molar teeth:--_Palæolagus_, with three species, from the Miocene of Dakota and Colorado; _Panolax_, from the Pliocene marls of Santa Fé; and _Praotherium_, from a bone-cave in Pennsylvania. The last-named genus has the crowns of the molars transversely oval, and without the enamel-band or crest which is seen on the surface of the teeth of other Hares. The LAGOMYIDÆ are known in a fossil state chiefly from Post-Pliocene deposits, and the bone breccias of caves in various parts of Europe. In Post-Pliocene times the genus _Lagomys_ seems to have been very generally distributed over the South of Europe; and the earliest appearance of the genus is in the Pliocene, three species having been described from deposits of that age at Œningen and Montpellier. The family is, however, carried further back in time by the genus _Titanomys_, in which the molars differ but slightly in structure from those of _Lagomys_, but there are only four of them in each series, both above and below. Two species of this genus have been recorded from Miocene deposits in France and Germany. [Illustration: SIDE VIEW OF SKULL AND LOWER JAW OF MESOTHERIUM CRISTATUM.] [Illustration: DENTITION OF MESOTHERIUM CRISTATUM. (A) Upper Jaw; (B) Lower Jaw; (C) Incisors.]