The Bermudas show no very marked relationship either to the N. American or to the West Indian fauna. In common with the former they possess a Polygyra, with the latter (introduced species being excluded) one species each of Hyalosagda, Subulina, Vaginula, and Helicina, so that, on the whole, they may be called West Indian. The only peculiar group is Poecilozonites, a rather large and depressed shell of the Hyalinia type.

(2) The Central American Sub-region may be regarded as extending from the political boundary of Mexico in the north to the isthmus of Panama in the south. It thus impinges on three important districts—the N. American, West Indian, and S. American; and it appears, as we should perhaps expect, that the two latter of these regions have considerably more influence upon its fauna than the former. Of the N. American Helicidae, Polygyra is abundant in Mexico only, and two species of Strobila reach N. Guatemala, while the Californian Arionta occurs in Mexico. S. American Helicidae, in the sub-genera Solaropsis and Labyrinthus, occur no farther north than Costa Rica. Not a single representative of any of the characteristic West Indian Helicidae occurs. Bulimulus and Otostomus, which form so large a proportion of the Mollusca of Venezuela, Colombia, Ecuador, and Peru, together with Orthalicus, are abundant all over the region. Again, Cylindrella, Macroceramus, and some of the characteristic Antillean operculates, are represented, their occurrence being in most cases limited to the eastern coast-line and eastern slope of the central range.

Besides these external elements, the region is rich in indigenous genera. Central America is remarkable for an immense number of large carnivorous Mollusca possessing shells. There are 49 species of Glandina, the bulk of which occur in eastern and southern Mexico; 36 of Streptostyla (S.E. Mexico and Guatemala, only 1 species reaching Venezuela and another Peru); 5 of Salasiella, 2 of Petenia, and 1 of Strebelia; the last three genera being peculiar. Streptaxis, fairly common in S. America, does not occur. Velifera and Cryptostracon, two remarkable slug-like forms, each with a single species, are peculiar to Costa Rica. Among the especial peculiarities of the region are the giant forms belonging to the Cylindrellidae, which are known as Holospira, Eucalodium, and Coelocentrum (Fig. [232]). They are almost entirely peculiar to Mexico, only 7 out of a total of 33 reaching south of that district, and only 1 not occurring in it at all.

Fig. 232.—Examples of characteristic Mexican Mollusca: A, Coelocentrum turris Pfr.; B, Streptostyla Delattrei Pfr.

The land operculates are but scanty. Tomocyclus and Amphicyclotus are peculiar, and Schasicheila, a form of Helicina, occurs elsewhere only in the Bahamas. Ceres (see Fig. [18], C, p. 21) and Proserpinella, two remarkable forms of non-operculate Helicinidae (compare the Chinese Heudeia), are quite peculiar. Pachychilus, one of the characteristic fresh-water genera, belongs to the S. American (Melaniidae) type, not to the N. American (Pleuroceridae). Among the fresh-water Pulmonata, the Aplecta are remarkable for their great size and beauty. In the accompanying table “Mexico” is to be taken as including the region from the United States border up to and including the isthmus of Tehuantepec, and “Central America” as the whole region south of that point.

Land Mollusca of Central America

Mexico
only.		Central
America
only.		Common to
both.
Strebelia1......
Glandina33133
Salasiella4...1
Streptostyla18126
Petenia...11
Limax...1...
Velifera...1...
Omphalina1011
Hyalinia253
Guppya...83
Pseudohyalina2...2
Tebennophorus1......
Cryptostracon...1...
Xanthonyx4......
Patula3...4
Acanthinula122
Vallonia...1...
Trichodiscus223
Praticolella1...1
Arionta3......
Lysinoe111
Oxychona25...
Solaropsis...2...
Polygyra1412
Strobila11...
Labyrinthus...5...
Otostomus23207
Bulimulus652
Berendtia1......
Orthalicus633
Pupa111
Vertigo1......
Holospira12......
Coelocentrum611
Eucalodium15...5
Cylindrella64...
Macroceramus21...
Simpulopsis21...
Caecilianella1......
Opeas123
Spiraxis821
Leptinaria...2...
Subulina234
Succinea1131
Vaginula1......
Aperostoma...41
Amphicyclotus212
Cystopoma2......
Tomocyclus...12
Choanopoma22...
Chondropoma211...
Helicina13106
Schasicheila2...1
Ceres2......
Proserpinella1......

(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.