If we draw a line immediately south of St. Croix and St. Bartholomew, we shall divide the Archipelago into two very different groups. The southern range of islands, or the Lesser Antilles, are, almost without exception, volcanic; beginning with the small detached volcanoes of Saba and St. Eustatius, and ending with the old volcano of Grenada. Barbuda and Antigua are low islands of Tertiary or recent formation, connected with the volcanic islands by a submerged bank at no great depth. The islands to the north and west are none of them volcanic; many are very large, and these have all a central nucleus of ancient or granitic rocks. We must also note, that the channels between these islands are not of excessive depth, and that their outlines, as well as the direction of their mountain ranges, point to a former union. Thus, the northern range of Hayti is continued westward in Cuba, and eastward in Portorico; while the south-western peninsula extends in a direct line towards Jamaica, the depth between them being 600 fathoms. Between Portorico and Hayti there is only 250 fathoms; while close to the south of all these islands the sea is enormously deep, from more than 1,000 fathoms south of Cuba and Jamaica, to 2,000 south of Hayti, and 2,600 fathoms near the south-east extremity of Portorico. The importance of the division here pointed out will be seen, when we state, that indigenous mammalia of peculiar genera are found on the western group of islands only; and it is on these that all the chief peculiarities of Antillian zoology are developed. _Mammalia._--The mammals of the West Indian Islands are exceedingly few, but very interesting. Almost all the orders most characteristic of South America are absent. There are no monkeys, no carnivora, no edentata. Besides bats, which are abundant, only two orders are represented; rodents, by peculiar forms of a South American family; and insectivora (an order entirely wanting in South America) by a genus belonging to a family largely developed in Madagascar and found nowhere else. The early voyagers mention "Coatis" and "Agoutis" as being {63}found in Hayti and the other large islands, and it is not improbable that species allied to _Nasua_ and _Dasyprocta_ did exist, and have been destroyed by the dogs of the invaders; though, on the other hand, these names may have been applied to the existing species, which do bear some general resemblance to these two forms. The Chiroptera, or bats, are represented by a large number of species and by several peculiar genera. The American family of Phyllostomidæ or vampires, has six genera in the Antilles, of which three, _Lonchorina_, _Brachyphylla_, and _Phyllonycteris_, are peculiar, the latter being found only in Cuba. The Vespertilionidæ have four genera, of which one, _Nycticellus_, is confined to Cuba. There are six genera of Noctilionidæ, of which one, _Phyllodia_, is confined to Jamaica.