49
ZOOLOGICAL
spiral shell within which the animal can wholly withdraw. The most important genera are Urocyclus, confined to tropical Africa; Parmarion, which is entirely Oriental; Helicarion, with about 100 species found principally in the Oriental and Australian Regions ; Ariophanta, with over 500 species of universal distribution ; Parmacella, occurring chiefly in the Mediterranean countries; Limax, with over 100 species of world-wide distribution; Vitrina, with about 100 species inhabiting chiefly the Northern Hemisphere; and Zonites, confined to Europe and America. The British forms of this family include nine species of Limax, one of Vitrina, and eleven of Zonites.
HELICIDiE (Typical Land-Snails). Plate 27, Map iii.
The typical Land-Snails occur in every part of the globe, and include an enormous number of species. The slugs of the genus Avion are included here, although sometimes placed in a separate family. Britain possesses three species, with numerous varieties of this genus, which is characterised by the absence of a shell. Curiously enough, these slugs, so abundant with us, are unknown in America. The typical genus Helix is an enormous one, with about 4000 species. Of universal distribution, this genus has been divided into innumerable sub-genera. Britain claims at least 25 species, each of which has several named varieties. Lastly, Bulimus, with over 300 species, is mainly South American.
BULIMULIDzE (Bulimulus, &c.). Plate 27, Map iii.
This family, as at present constituted, is confined to the New World, the Oriental Region, and the Australian Region. It contains several species which were formerly placed in the genus Bulimus (Helicidse), but which, owing to certain characters formerly overlooked, are more properly removed from that position. The great majority of the members of the family belong to the typical genus Bulimulus.
UROCOPTIDiE (Uroeoptis, &c.). Plate 27, Map iii.
This family, formerly bearing the name Cylindrellidse, is entirely confined to tropical America, Their shells are very long, with many whorls, and often beautifully sculptured. About 250 species have been described, TJrocoptis (or Cylindrella) containing about 200, and Maaroceramus most of the remainder.
PUPIDzE (Pupa, &c.). Plate 27, Map iii.
This group is a very extensive and somewhat heterogeneous one, containing representatives in all parts of the world. The typical genus, Pupa, contains about 400 species found universally, but more characteristic of temperate regions. Several species occur in Britain. Vertigo has an equally extensive distribution, with about 100 species; while Clausilia contains at least 700 species, which are mainly inhabitant#of Europe and Asia, with five in Britain. Of other genera, Anostoma, Odontostomus, Megaspira and Strophia are American; Buliminus belongs to the Old World; Balea is European; while Codiaxis is confined to the Solomon Islands and Australia.
STENOGYRIDiE (Agate-Snails, &c.). Plate 27, Map iv.
Over 500 species of this family are known, and these have a world-wide distribution. The genus Achatina is probably the most important, containing about 80 species, which are confined to the Ethiopian region, and known as Agate-Snails. Their shells are handsomely marked, and among them are the largest land-shells known. Stenogyra, the typical genus, contains 250 species of universal distribution; while Ferussacia is an interesting genus, confined principally to the Mediterranean region, the Canary Islands, Madeira, and the Malay Archipelago.
SUCCINEIDzE (Amber-Snails, &c.). Plate 27, Map iv.
The Succineidee are found all over the world, and contain over 200 species, the great majority of which constitute the typical genus, Succinea. Half a dozen species of this genus occur in Britain. The molluscs of this family may be called subaquatic, since they live in damp places, on aquatic plants, or in marshes. The genus Homalonyx, with about half a dozen species, is confined to the West Indies and Brazil; while Hyalimax has a still more limited distribution, occurring only in Mauritius and the Nicobar Islands.
LIMNzEID.3¡ (Fresh-water Limpets, &c.). Plate 27, Map iv.
The molluscs of this family are inhabitants of fresh-water, but at the same time are air-breathers, and hence come to the surface at intervals to renew their supply of free oxygen. The family, as a whole, has a universal distribution, as have also the principal genera Ancylus (Eresh-water Limpets), Planorbis and Limnsea (Pond-Snails). Of these three genera Britain possesses two, twelve, and eight species respectively. Gundlachia (five species) is found in the United States, Cuba, and Tasmania; Latia (two species) is confined to New Zealand; Pompholyx is Californian; while Choanomphalus is only found in Lake Baikal, occurring in that lake at a depth of over 1000 feet.
PHYSIDjE (Physa, &c.). Plate 27, Map iv.
Although a comparatively small group, the Pond-Snails of this family have an almost universal distribution. The two principal genera are Physa, with about 100 species, and Aplecta, with about 25. In Britain the two species, Physa fontinalis and Aplecta hypnorum, alone represent the family, the latter being abundant and widely distributed in slow rivers, canals and ditches.
CEPHALOCHORDATA.
BRANCHIOSTOMATIDzE (Lancelets). Plate 26, Map vi.
The fish-like and primitive vertebrates known as Lancelets are of so peculiar a structure as to constitute a separate class to themselves of an importance, from a morphological point of view, equal to that of the whole of the fishes. They are marine animals, and the 16 known species are found on the coasts of all parts of the world. Most of the records, however, are tropical and subtropical, referring to localities between 40° N. and 40° S. Branchiostoma lanceolatum has been recorded from many parts of the British coast.
CLASS MOLLUSC A (Molluscs).
ORDER CEPHALOPODA
OCTOPODID^I (Octopus, &c.). Plate 27, Map i.
The Octopodidse occur off the coasts of nearly all temperate and tropical regions. About 100 species have been described, and two at least occur in British waters. They are solitary animals, inhabiting rocky shores, and the adults attaiif a huge size, some having been seen over 9 feet in length. Their food consists principally of bivalved molluscs. In the South of Europe they are sold as food, and are said to be excellent eating.
ARGONAUTIDiE (the Paper-Nautili). Plate 27, Map i.
The members of this family are all placed within a single genus (Argonauta). They inhabit the warmer portions of all seas, and are reported to be more active in the night. The shell of these creatures is a very beautiful object, and was at one time supposed to be made by some other mollusc, the Paper-Nautilus merely using it as a convenient dwelling-place. It is now known, however, to be secreted by the animal itself. The male is without a shell, and is a much smaller creature than the female.
LOLIGINIDzE (Squids). Plate 27, Map i.
The Squids or Calamaries, of which about 60 species are known, occur in all seas. Three species are found in British seas, including the Common Squid (Loligo vulgaris). The Cuttle-fishes of this family sometimes grow to an enormous size. Specimens have been captured which, when measured, were found to possess a body at least 7 feet long, with arms that stretched a distance of from 24 to 30 feet.
SEPIIDzE (True Cuttle-Fishes). Plate 27, Map i.
Over 30 species of this family are known, which are found in the seas of all the world. They are, in general, much smaller than the members of the preceding family, seldom exceeding a foot in length. Three species of Sepia find a place on the British list, the best-known of which is usually called the Common Cuttle-fish (S. officinalis). They are chiefly shore animals, feeding on fish and crustaceans. In Italy they are much esteemed as food.
SPIRULIDzE (Spirula). Plate 27, Map ii.
Three species of this interesting family are known, all belonging to a single genus (Spirula). The shells of these animals are well-known, since they are washed ashore in all parts of the world. The living animal is, however, very rarely seen, and very few good specimens have been obtained. The best-known form is S. peronii, which is reported from British waters.
NAUTILIDzE (Nautili). Plate 27, Map ii.
The six living species of this family are confined to tropical seas, and little is known of their habits. In many of the Polynesian Islands these molluscs are used as food, while their elegant shells are in India made into drinking-cups. The Nautili are the sole existing representatives of a group which is known as Tetrabranchiate, and which includes many thousands of species only known in a fossil state. The well-known Ammonites of the fossil collector are referred by many authors to this group.
CLASS GASTROPODA.
ORDER PULMONATA.
TESTACELLIDzE (Shelled Slugs). Plate 27, Map ii.
This family of terrestrial molluscs possesses representatives in all the zoogeographical regions, including two species which are on the British list, though probably introduced. These belong to the typical genus (Testacella), which contains besides a few species found in the South of Europe and North Africa. Streptostylus is confined to tropical America, with about 50 species ; Glandina, with about 150 species, is likewise chiefly American ; Gibbus, with over 40 species, is confined to Madagascar, Seychelles, and the neighbouring islands ; while Paryphanta and Bhytida are confined to the Australian region.
LIMACIDiE (True Slugs). Plate 27, Map ii.
This is an extensive group, containing representatives in all parts of the world. Some of the slugs belonging to this family are devoid of an external ׳ shell, possessing only a small internal plate; others again possess a complete
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