The Xiphodon differs from that just described in having the inferior molars tuberculous, and being without the additional or false hoof on the fore feet. It contains but a single species (A. gracile), which, judging from the length and smallness of its limbs, and the elevation of the tarsus, must have presented in every respect a complete contrast to the A. commune, exhibiting the light form and graceful proportions of the gazelle. Its course must necessarily have been rapid, and probably unembarrassed by a long tail; and, instead of resorting habitually to the rivers and ponds, like the former species, it must have been confined to the dry land, and, probably like the gazelles and antelopes, fed upon dry aromatic herbs, and was pro vided with long moveable ears to warn it of the approach of danger.
The third sub-genus, Dichobunes, contains three species, all esta blished from the observation of detached bones, and of the actual forms of which it is consequently impossible to give a correct idea. They differed from the species contained in the two former subdivisions, principally by having a small additional or false hoof both on the fore- and hind-feet; and this character is so well marked in all the sub-genera of M. Cuvier, that, besides other considerations, it would suffice, among existing animals, to distinguish three separate genera, and perhaps should do so in the present instance. The Diehobtoies were all of small stature : the largest of the three known species (A. leporinum) was about the size of a hare; the other two (A. nvurinurn and A. obliquum) about that of the guinea-pig, were in all probability the smallest of hoofed quadrupeds. M. Cuvier
supposes them to have been the hares and rabbits of the proadamite world, but their whole structure seems to approximate them more correctly to the musks of the present time, and they probably differed little from these animals either in form or habits. Another species of this genus was discovered by Mr. Pratt, in the Eocene deposits at Briustead in the Isle of Wight, and has been described by Professor Owen under the name of D. cervinum.
( Cuvier, 088ellierld Possiles ; Owen, British, Fossil Mammals.) ANOPLURA, a family of Insects, including the Aptera of Linnaeus, and the various forms of Pediculus PEDICIATI8 and Parasitic Insects of other authors. The researches which were commenced on this family by Dr. Leach have been carried on by Mr. Denny, and resulted in the discovery of a vast number of new forms. The result is that it has been found that every animal is infested with, or, for some wise purpose is accompanied by, one or more creatures belonging to this family, having a peculiar form in each species. Nearly 500 different forms of these curious insects, all formed on the type of the common human louse, have been described by Mr..Denny, in the catalogue of the specimens which at present exist in the British Museum. In most cases but one species of the parasite exist on one species of animal, but there are instances, as in the eagles and gulls, in which a species of the bird is attacked by five species of A noplura. The best series of illustrations of these insects which exist are contained in Denny's Anoplura Britannica,' published in 1842.