342 



THE NEOTROPICAL REGION 



CHAP. 



L. Baikal. Bithynia^ absent from the Eastern States, is repre- 

 sented by two species. The general indications are in favour of 

 the Californian fauna having migrated from an Old World source 

 after the upheaval of the Sierras ; the American fauna, on the 

 other hand, is purely indigenous, with no recent Old World 

 influence at all. 



Land Mollusca of the Nearctie Region 



F. The Neotropical Region 



The land Mollusca of the Neotropical Region stand in com- 

 plete contrast to those of the Nearctie. Instead of being scanty, 

 they are exceedingly abundant ; instead of being small and 

 obscure, they are among the largest in size, most brilliant in 

 colour, and most singular in shape that are known to exist. At 

 the same time they are, as a whole, isolated in type, and exhibit 

 but little relation with the Mollusca of any other region. 



The most marked feature is the predominance of the peculiar 

 genera Bulimus and Bulimulus^ the centre of whose develop- 

 ment appears to lie in Peru, Ecuador, and Bolivia, but which 

 diminish, both in numbers and variety of form, in the eastern 

 portion of the region. In the forests of Central America, 

 Venezuela, and Ecuador, and, to a lesser degree, in those of Peru 

 and Brazil, occurs the genus Orthalicus^ whose tree-climbing 

 habits recall the Cochlostyla of the Philippines. These three 

 groups of bulimoid forms constitute, as far as the mainland is 

 concerned, the preponderating mass of the land Mollusca. Helix 

 proper is most strongly developed in the Greater Antilles, which 

 possess several peculiar groups of great beauty. In Central 

 America Helix is comparatively scarce, but in the northern 

 portions of the continent several fine genera QLabyrinthus, 



