| Pigmy African Flying-Squirrel (Idiurus zenkeri). |
FLYING-SQUIRREL, properly the name of such members of the squirrel-group of rodent mammals as have a parachute-like expansion of the skin of the flanks, with attachments to the limbs, by means of which they are able to take long flying-leaps from tree to tree. The parachute is supported by a cartilage attached to the wrist or carpus; in addition to the lateral membrane, there is a narrow one from the cheek along the front of each shoulder to the wrist, and in the larger species a third (interfemoral) connecting the hind-limbs with the base of the long tail. Of the two widely distributed genera, Pteromys includes the larger and Sciuropterus the smaller species. The two differ in certain details of dentition, and in the greater development in the former of the parachute, especially the interfemoral portion, which in the latter is almost absent. In Pteromys the tail is cylindrical and comparatively thin, while in Sciuropterus it is broad, flat and laterally expanded, so as to compensate for the absence of the interfemoral membrane by acting as a supplementary parachute.
In general appearance flying-squirrels resemble ordinary squirrels, although they are even more beautifully coloured. Their habits, food, &c., are also very similar to those of the true squirrels, except that they are more nocturnal, and are therefore less often seen. The Indian flying-squirrel (P. oral) leaps with its parachute extended from the higher branches of a tree, and descends first directly and then more and more obliquely, until the flight, gradually becoming slower, assumes a horizontal direction, and finally terminates in an ascent to the branch or trunk of the tree to which it was directed. The presence of these rodents at night is made known by their screaming cries. Sciuropterus is represented by S. velucella in eastern Europe and northern Asia, and by a second species in North America, but the other species of this genus and all those of Pteromys are Indo-Malayan. A third genus, Eupetaurus, typified by a very large, long-haired, dark-grey species from the mountains to the north-west of Kashmir (Eu. cinereus), differs from all other members of the squirrel-family by its tall-crowned molar teeth. It has a total length of 37 in., of which 22 are taken up by the tail.
In Africa the name of flying-squirrel is applied to the members of a very different family of rodents, the Anomaluridae, which are provided with a parachute. Since, however, this parachute is absent in some members of the family, the most distinctive character is the presence of a double row of spiny scales on the under surface of the tail, which apparently aid in climbing. The flying species are also distinguished from ordinary flying-squirrels by the circumstance that the additional bone serving for the support of the fore part of the flying-membrane rises from the elbow-joint instead of from the wrist. The family is represented by two flying genera, Anomalurus and Idiurus; the latter containing only one very minute species (shown in the cut) characterized by its small ears and elongated tail. Most of the species are West African. In habits these rodents appear to be very similar to the true flying-squirrels. The species without a parachute constitutes the genus Zenkerella, and looks very like an ordinary squirrel (see [Rodentia]).
In Australia and Papua the name flying-squirrel is applied to such marsupials as are provided with parachutes; animals which naturalists prefer to designate flying-phalangers (see [Marsupialia])
(R. L.*)
FLYSCH, in geology, a remarkable formation, composed mainly of sandstones, soft marls and sandy shales found extending from S.W. Switzerland eastward along the northern Alpine zone to the Vienna basin, whence it may be followed round the northern flanks of the Carpathians into the Balkan peninsula. It is represented in the Pyrenees, the Apennines, the Caucasus and extends into Asia; similar flysch-like deposits are related to the Himalayas as the European formations are to the Alps. The Flysch is not of the same age in every place; thus in the western parts of Switzerland the oldest portions probably belong to the Eocene period, but the principal development is of Oligocene age; as it is traced eastward we find in the east Alps that it descends into the upper Cretaceous, and in the Vienna region and the Carpathians it contains intercalations which clearly indicate a lower Cretaceous horizon for the lower parts. It appears indeed that this type of formation was in progress of deposition at one point or another in the regions enumerated above from Jurassic to late Tertiary times. The absence of fossils from enormous thicknesses of Flysch makes the correlation with other formations difficult; often the only indications of organisms are the abundant markings supposed to represent Algae (Chondrites, &c.), which have given rise to the term “Hieroglyphic-sandstone.” The most noteworthy exceptions are perhaps the Oligocene fish-bed of Glarus, the Eocene nummulitic beds in Calabria, and the Aptychus beds of Waidhofen. Local phases of the Flysch have received special names; it is the “Vienna” or “Carpathian” sandstone of those regions; the “macigno” (a soft sandstone with calcareous cement) of the Maritime Alps and Apennines; the “scagliose” (scaly clays) and “alberese” (limestones) of the same places are portions of this formation. The gris de Menton, the gris d’Annot of the Basses Alps, and the gris d’Embrun of Chaillot appear in Switzerland as the gris de Taveyannaz. At several places the upper layers of the Flysch are iron-stained, as in the region of Léman and at the foot of the Dent du Midi; it is then styled the “Red-Flysch.” Lenticular intercalations of gabbro, diabase, &c., occur in the Flysch in Calabria on the Pyrenees. Large exotic blocks of granite, gneiss and other crystalline rocks in coarse conglomerates are found near Vienna, near Sonthofen in Bavaria, near Lake Thun (Wild Flysch) and at other points, which have been variously regarded as indications of glaciation or of coastal conditions.