(_a_) The _Senegambian Province_ may be regarded as extending from the mouth of the Senegal River to Cape Palmas. Only 8 genera of land Mollusca are known, including 4 _Limicolaria_ and 3 _Thapsia_, with 1 small _Cyclophorus_. Fresh-water genera are abundant, and include most of the characteristic Ethiopian forms. (_b_) The _West African Province_ extends from Cape Palmas to the mouth of the Congo, and is rich in Mollusca. The great _Achatina_, largest of land snails, whose shell sometimes attains a length of 6½ in., _Limicolaria_, _Perideris_, and _Pseudachatina_ are the characteristic forms. The Agnatha are represented by _Ennea_, _Streptaxis_, and _Streptostele_. _Rachis_ and _Pachnodus_, sub-genera of _Buliminus_, occur also on the east coast. A special feature is the development of several peculiar slug-like genera, _e.g._ _Oopelta_, perhaps a form of _Arion_; _Estria_, a slug with an external shell, akin to _Parmacella_; and _Aspidelus_, a form intermediate between _Helicarion_ and _Limax_. _Claviger_, a handsome group akin to _Cerithium_, is peculiar to the estuaries of West African rivers. About sixteen species are known from the _Cameroons District_, but no peculiar genera occur. The _French Congo District_ has not yet been well explored. _Tomostele_, a genus allied to _Streptostele_, is peculiar, and _Pseudachatina_ attains its maximum. [Illustration: FIG. 217.--_Columna flammea_ Müll., Princes I.] _St. Thomas and Princes Is._, in the Gulf of Guinea, are well known. Princes I. has 22 species, 14 peculiar, and 2 common to St. Thomas only, one of the latter being the great sinistral _Achatina bicarinata_ Chem. The remarkable genus _Columna_ (Fig. 217) is peculiar, and _Streptostele_ (4 sp.) attains its maximum. Peculiar to St. Thomas are _Pyrgina_, a turreted form of _Stenogyra_; _Thyrophorella_, a sinistral form of _Zonites_; and _Atopocochlis_, a large bulimoid shell, whose true relationships are not yet known. _Homorus_, a group of _Achatina_ with an elongated spire, occurring also in the Angola District and on the east coast, has 4 species. No fresh-water species have as yet been discovered in either of the islands. The _Angola and Benguela District_, extending from the Congo to the Cunene R., probably belongs to the West African Sub-region, but until its fauna is better known it is advisable to consider it apart. _Achatina_ continues abundant, but the other characteristic West African forms (_Pseudachatina_, _Streptostele_, _Perideris_) diminish or are absent altogether. No _Helix_ and only 1 _Cyclophorus_ occur. _Ovampo_, _Damara_, and _Great Namaqualand_, lying between the Cumene and Orange rivers, seem to form a transition district between the West and South African faunas. _Helix_ reappears, while the characteristic West African genera are almost entirely wanting.