(3) =The Colombian Sub-region= includes Colombia, New Grenada, Venezuela, Guiana, Ecuador, Peru, and Bolivia. It has been usual to separate off the two latter countries as forming a distinct “Peruvian” sub-region; but there is, as will be seen, absolutely no line to be drawn between the Mollusca of Peru and those of Ecuador; nor would one, on geographical considerations, expect to be able to draw such a line. A better method of subdivision, so far as the species of the whole eastern portion of the region are concerned, would be to group the Mollusca according to the altitude at which they occur, were it not that the evidence on this point is at present but fragmentary. We know, however, that all along the line of the Andes certain species, more particularly of _Bulimulus_, occupy their own zones of elevation, some ascending as high as 10,000 feet above the sea, and never occurring on the plains. In the northern portions of this sub-region, Central American and West Indian influence is felt to a certain extent. Thus there are eight _Glandina_ and one _Streptostyla_ in Venezuela and Colombia together with one or two species of _Cistula_, _Chondropoma_, _Proserpina_, and _Cylindrella_, while a single _Strophia_ (decidedly a straggler) occurs at Curaçao. In Demerara and Cayenne there are three or four species of _Dentellaria_. In Ecuador, however, _Glandina_ diminishes to three species, and in Peru disappears altogether, although one _Streptostyla_ occurs. Similarly the West Indian operculates are reduced to one _Chondropoma_ (Ecuador) and disappear entirely in Peru. [Illustration: FIG. 233.--=A=, _Orthalicus Deburghiae_ Reeve, Ecuador; =B=, _Bulimus_ (_Pachyotus_) _egregius_ Jay, Brazil.] The Helicidae are most abundant in the north and west, and are represented by several very striking sub-genera, some of which possess remarkably toothed apertures, and perhaps betray an ancestry common to some of the West Indian genera. Of these, _Labyrinthus_ has 12 species in Venezuela and Colombia, 5 in Ecuador, and 3 in Peru and Bolivia; _Isomeria_ 12 in Venezuela and Colombia, 20 in Ecuador, and 2 in Peru and Bolivia; _Salaropsis_ is represented in these countries by 6, 3, and 7 species, and _Systrophia_ by 4, 5, and 8 species respectively. _Clausilia_--in the group _Nenia_--appears in some numbers along the Andes chain, the only other representative in the New World being the solitary species occurring at Porto Rico. There have been described, from Venezuela and Colombia 10 species, from Ecuador 5, and from Peru and Bolivia 12. Another marked feature of the region is the occurrence of the Orthalicidae, in the two genera _Orthalicus_ and _Porphyrobaphe_. The latter of these magnificent forms is peculiar, while the former reaches Mexico, the West Indies, and Brazil. Ecuador, which contains 23 species, seems the metropolis of the group.