| Hyalinia | 1 |
| Patula | 4 (3 extinct) |
| Endodonta | 10 (7 extinct) |
| Bulimulus | 7 (5 extinct) |
| Pachyotus | 1 (extinct) |
| Tomigerus (?) | 1 (extinct) |
| Pupa | 2 (extinct) |
| Succinea | 3 |
The 5 genera which concentrate our attention are Patula, Endodonta, Pachyotus (Fig. [222]), Tomigerus, and Bulimulus, all of which appear utterly strange to an oceanic island in the middle of the S. Atlantic. Patula and Endodonta are essentially Polynesian forms, occurring abundantly on all the island groups in the Central Pacific. Pachyotus, Tomigerus (assuming its correct identification), and Bulimulus are all S. American forms, the two former being especially characteristic of Brazil. How this mixture of genera now confined to regions so widely distant, not only from St. Helena itself, but from one another, became associated here, is a problem obviously not easy of solution. The fauna is probably a remnant of a very ancient type, possibly at one time much more widely distributed. Endodonta (an essentially insular form, like Omphalotropis) actually occurs on Fernando Noronha, off the Brazil coast, and we shall see how an Indian and even a Polynesian element is present off the eastern coasts of Africa.
Ascension I.—One indigenous species, a so-called Limax, is all that has ever been discovered.
(3) The Malagasy Sub-region includes Madagascar with its attendant satellites Bourbon, Mauritius, and Rodriguez, and the Seychelles and Comoro groups. No land Mollusca are known from the Amirantes, the Chagos, or from Aldabra. The special characteristics of the sub-region are the great development of the carnivorous land Mollusca (Ennea, Gibbus), the occurrence of a considerable number of true Helicidae of great size and beauty, and the prominence of the genus Cyclostoma.
(a) The Madagascan Province.—The land Mollusca of Madagascar, although as yet imperfectly known, possess a striking individuality. Two of the chief characteristics of the Ethiopian region are the paucity of its land operculate and of its Helix fauna; Madagascar is especially distinguished by the rich development of both these groups. For size, colouring, and beauty of shape, the Helicidae of the two sub-genera Ampelita and Helicophanta rival, if they do not surpass, any in the world. They are quite peculiar to this sub-region, not a trace of them occurring on the Mascarenes, Seychelles, or even on the Comoros. Helicophanta is distinguished by the enormous size of its embryonic shell, which persists in the adult (Fig. [223]), and in this respect the group appears to be related to Acavus (Ceylon, Fig. [204]) and Panda (N.E. Australia). As is usual when Helix is well developed, Nanina (about 12 sp.) is proportionately scanty.
The African Bulimini (Pachnodus and Rachis) are represented by two species, but Achatina, so abundant on the mainland, is scarce. Two other groups of Buliminus, Leucotaenia and Clavator, are peculiar. The presence of a single Kaliella, specifically identical with a common Indian form, is very remarkable.
Cyclostoma proper, of which Madagascar is the metropolis, is richly developed (54 sp.). Many of the species are of great size and of striking beauty of ornamentation. Unlike its Helicidae, this genus is not restricted to Madagascar; several species occur on the mainland, 6 on the Comoros, one on the Seychelles, and 16 in Mauritius. The sub-genera Acroptychia and Hainesia are peculiar.
Fig. 222.—Pachyotus auris vulpina Desh., St. Helena (sub-fossil).
