202 ON THE GEOGRAPHICAL 



plains or close brakes, of which no species exists in New 

 Holland, while those of Southern Africa depart from the 

 t}^ical species. The Tree-Serpents are more especially 

 peculiar to equatorial countries ; but, as they inhabit vast 

 forests, or well wooded countries, they are not found in 

 countries Avhere those necessary conditions of their exist- 

 ence are not met with. This is probably the reason why 

 these serpents have not been observed in the greatest part 

 of New Holland, and that Southern Africa supports but 

 a single species of this family, anomalous besides, and ap- 

 proaching to the genus Coluber. The three genera which 

 compose this family of tree-serpents, are found in both 

 worlds ; but it is remarkable, that the Dipsas of America 

 never arrives at that great size which is observed in most 

 of the Indian species, and that the Dryiophis of both 

 Americas form a true geogi-aphical division in this, that 

 they have the dentary system and the muzzle less de- 

 vch)ped, and that the pupil of the eye is orbicular. The 

 fresh-water serpents which arc comprehended in the two 

 genera, Tropidonotus andHoMALOPSis, are found in abun- 

 dance in countries rich in lakes, or watered by numerous 

 rivers. Hence it is that these animals are common in 

 Asia, in America, and even in Europe, that they are pro- 

 bably not met with at all in New Holland, and that they 

 are scarce in Africa ; for there exists but a single species 

 of Tropidonotus in the southern parts of that vast conti- 

 nent, and even this species presents an organization 

 wholly anomalous. The Homalopsis even, which are pre- 

 eminently fresh-water snakes, and essentially aquatic, and 

 which belong to warm countries, have not been observed 

 in New Holland, nor in Africa, whilst they abound in both 

 Americas ; they even replace, in South America, the Tro- 

 pidonotus, which has not yet been discovered in that vast 

 peninsula. The geogi'aphic distribution of the genus Boa 

 presents us with several facts worthy of notice. They are 

 also serpents peculiar to hot climates. The true Boas are 

 only found in South America ; they are replaced in the 

 old world by Pythons ; but we find in the Indies several 

 serpents very analogous to the Boa, but of very small 

 size, and of which there does not exist in the whole west- 



