DISTRIBUTION OF FAMILIES. 29 



appearing at localities separated from each other by nearly half of 

 the earth's circumference. 



Distribution of Families. The restriction of families to cer- 

 tain local areas is of comparatively rare occurrence, an almost neces- 

 sary consequence of the number of species and genera of which they 

 are in most cases composed. Among mammals the Cheiromydge, 

 with one genus and one species, the aye-aye (Cheiromys Madagas- 

 cariensis), are confined exclusively to the Island of Madagascar ; the 

 Protelidse, likewise consisting of but a single genus and species, the 

 aard-wolf (Proteles Lalandii), an animal in several respects inter- 

 mediate between the cats and dogs, and considered by some as 

 representing a greatly modified form of hyena, are confined to the 

 extra-tropical regions of South Africa. Occupying pretty nearly 

 the same region, and confined to it, are the Chrysochloridse, or 

 golden-moles, with a single genus and about five species. The 

 Ailuridse, a group of animals having then* nearest allies in the 

 coatis and bears, and consisting of one or two species, appear to 

 be restricted to the forest region of Eastern Thibet and the Eastern 

 Himalaya. Among the class Aves we have likewise families that are 

 restricted both as to the number of species comprised by them and 

 the region which they inhabit. The Paictidae, a group of birds, 

 considered by some ornithologists to have affinities with the Ameri- 

 can ant-thrushes (Formicariidae), and by others with the Old-World 

 pittas, consist of a single genus and two or more species, both of 

 which are confined to the Island of Madagascar. Here, also, ex- 

 clusively belong the Leptosomidse, birds allied to the cuckoos and 

 rollers. The Apterygidse, with one genus (Apteryx) and four species, 

 are strictly confined to the two larger islands of New Zealand ; the 

 Drepanidae, with some four or five genera and ten species, are re- 

 stricted to the Sandwich Island group ; and, finally, the paradise- 

 birds, excluding the bower-birds, which are classed together with 

 them in one family by some ornithologists, with about eighteen 

 genera and thirty species, 8a are almost entirely confined to New 

 Guinea and the surrounding islands, only four representatives of the 

 group finding their way into the neighbouring continent of Australia. 

 Mr. Wallace has emphasised the very remarkable case of localisation 

 presented among reptiles by the Uropeltidae, or rough-bellied, bur- 

 rowing snakes, all of whose members appear to be strictly con- 

 fined to Ceylon and the adjacent parts of the Peninsula of India. 9 



