Fig. 200.—A, Buliminus (Petraeus) labrosus Oliv., Beyrout; B, Buliminus (Chondrula) septemdentatus Roth., Palestine.
Upper Mesopotamia appears to possess a mixture of Syrian and Caucasian forms, including a Parmacella. Lower Mesopotamia has an exceedingly poor land fauna, but is comparatively rich in fresh-water species, the growing eastern character of which is shown by the occurrence of several Corbicula and Pseudodon, and of a Neritina of a distinctly Indian type.
(b) The Pontic province extends from Western Austria to the Sea of Azof, and includes Austria, Hungary, Roumania, the Balkan peninsula (so far as it does not form part of the Mediterranean sub-region), the islands of the Greek Archipelago, southern Russia and the Crimea, and Asia Minor. It thus practically corresponds to the whole Danube basin, together with the lands bordering on the Black Sea, except at the extreme east, which belongs to the Caucasian sub-region. Fischer separates off Greece, Asia Minor (except the northern coast-line), and the intervening islands, with Crete and Cyprus, as constituting a portion (Hellado-Anatolic) of the Mediterranean sub-region proper. These districts, however, appear to possess scarcely sufficient individuality to warrant their separate consideration.
A prominent characteristic of the Pontic Mollusca is the great abundance of Clausilia and Buliminus. In the islands east and west of Greece Clausilia forms a large proportion of the fauna, each island, however small, possessing its own peculiar forms. The Helices belong principally to the groups Campylaea (which is very abundant in Austro-Hungary), Pomatia (Greece and Asia Minor), and Anchistoma. Macularia is comparatively scarce, but is represented in Greece by one very large form (Codringtonii Gray). Zonites proper has its metropolis in this sub-region, and the Danube basin contains one or two species of Melania and Lithoglyphus. Buliminus is abundant throughout the sub-region, in the sub-genera Zebrina, Napaeus, Mastus, and Chondrula. Several striking forms of Zebrina (Ena) are peculiar to the Crimea.
(c) The Caucasian Province.—The limits of this province can hardly be exactly defined at present. It appears, however, to include the whole line of the Caucasus range, Armenia, and North Persia.
The land Mollusca are abundant and interesting. Among the carnivorous genera are four species of Daudebardia, a Glandina, and three peculiar forms of naked slug, Pseudomilax, Trigonochlamys, and Selenochlamys. There is a single Parmacella, the same species as the Mesopotamian, and a good many forms of Limax. Vitrina and Hyalinia are well represented, and the predominant groups of Helix are Euloto, Cartusiana, Xerophila, and Fruticocampylaea, the last being peculiar. Clausilia and Pupa are rich in species, together with Buliminus of the Chondrula type. One Clausilia of the Phaedusa section, together with a Macrochlamys (Transcaspian only), a Corbicula, and a Cyclotus, show marked traces of Asiatic affinity. There is one species each of Acicula and Cyclostoma, and one of Pomatias.
The Caspian Sea, like Lakes Baikal and Tanganyika, is distinguished by the possession of several remarkable and peculiar genera. The sea itself, the waters of which are brackish, is 80 feet below the level of the Black Sea, and is no doubt a relict of what formed, in earlier times, a very much larger expanse of water. Marine deposits containing fauna now characteristic of the Caspian, have been found as far north as the Samara bend of the Volga. It is probable, therefore, that in Post-pliocene times an arm of the Aralo-Caspian Sea penetrated northward up the present basin of the Volga to at least 54° N. The Kazan depression of the Volga (55° N.) also contains characteristic Caspian fossils.[367] According to Brusina,[368] the Caspian fauna, as a whole, is closely related to the Tertiary fauna of southern Europe.
Twenty-six species of univalve Mollusca, the majority being modified forms of Hydrobia, have been described from the Caspian, namely, Micromelania (6), Caspia (7), Clessinia (3), Nematurella (3), Lithoglyphus (1), Planorbis (1), Zagrabica (1), Hydrobia (2), Neritina (2). The bivalves are mostly modified forms of Cardium (Didacna, Adacna, Monodacna), which also occur in estuaries along the north of the Black Sea. A form of Cardium edule itself occurs, and numberless varieties of the same species are found in a semi-fossil condition in the dry or half dry lake-beds, which are so abundant throughout the Aral district.
(d) The Atlantidean province consists of the four groups of islands, the Madeiran group, the Canaries, the Azores, and the Cape Verdes.
The Madeiran group contains between 140 and 150 species of Mollusca which may be regarded as indigenous, the great majority of which are peculiar. Only 11 species are common to Madeira and to the Azores, and about the same number, in spite of their much greater proximity, to Madeira and the Canaries. No less than 74 species, or almost exactly one-half, belong to Helix, and 9 to Patula. A considerable number of the Helices are not only specifically but generically peculiar, the genera bearing close relationship to those occurring in the Mediterranean region. As a rule they are small in size, but often of singular beauty of ornamentation. Various forms of Pupa are exceedingly abundant (28 sp.), as is also Ferussacia (12 sp.). There are also 3 Clausilia (which genus occurs on this group alone), and 3 Vitrina (a genus which occurs on all the groups). The land operculates are represented solely by 4 Craspedopoma, which is common to all the groups except the Cape Verdes.