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characters ascribed to them in the preceding family. The first pleopods are absent or reduced to widely separated rudiments, of doubtful homology. The pleopods of the second, third, fourth, and fifth segments are two-branched; the second pair have the usual stilets in the male. On each opercular plate there is a roundish air-cavity placed near the outer margin, with a single opening in each operculum of the second pleopods, but two openings in those of the three following pairs. According to von Ebner, the peduncle in the pleopods forms a part of the branchial sack, so that the two branches instead of being freely articulated with it are fastened direct to the segment. The uropods are similar to those in the Tylidæ, but are attached at the front corner of the outer margin instead of at its centre. The minute terminal joint is considered to be the outer branch.

Helleria, Ebner, 1868, is the only genus, and Helleria brevicornis, Ebner, the only species. It occurs in Italy, and in the mountain forests of Corsica in damp moss; also M. Chevreux has recently sent it me from Cap d'Antibes out of his own garden. In 1879 Budde-Lund changed the name Helleria to Syspastus, because other genera of Crustaceans have received the name Helleria, but these other genera, as M. Chevreux has pointed out, were named not before but after the publication of von Ebner's genus. It would be absurd that Dr. Camil Heller should be entirely deprived of the honour intended him, through the fact that so many of his friends had separately endeavoured to render it. Without question von Ebner's genus must retain its original name, and, with the cancelling of Syspastus, BuddeLund's family 'Syspasti' naturally suffers a corresponding change into Helleriidæ. The figures on Plate XIX. are copied from von Ebner's paper.

Family 4.-Oniscidae.

The animal is seldom very convex or capable of easily assuming a globular form. The head is little broader than long, and not clearly flanked by the first segment of the

peræon; the face is sloping. The sides of the head are distinctly marked by a vertical marginal line and an inframarginal line. The clypeus is arched.' The pleon has six segments, of which the first two are narrower and usually shorter than the third. The young quit the mother with the seventh segment of the peræon still undeveloped. The first antennæ are three-jointed. The second antennæ have the flagellum from two- to four-jointed. The first maxillæ have two plumose setæ on the inner plate; the second maxillæ have two plates; the 'palp' of the maxillipeds is two-jointed, the epipod oblong, acute. The trunkfeet are rather long. In the first and second pleopods of the male the inner branches form long narrow sexual organs, those of the first pair often coalesced; in the female the same branches are rudimentary, short, acute. In the remaining pairs the inner branch is branchial; in all the pairs the outer branch is opercular, and often also tracheal. The uropods are always prolonged beyond the two terminal segments of the pleon.

Budde-Lund, in his exceedingly valuable work on the Terrestrial Isopoda, makes a family Onisci, which he divides into two sections, Armadilloidea and Oniscoidea, but it seems better to constitute two families, since it is the almost invariable fate of large sections eventually to be made independent. For the Oniscidæ, or second section, Budde-Lund gives a tantalising 'Conspectus Generum,' based on the flagellum of the second antennæ, on the tracheal or non-tracheal character of the pleopods, and on the uropods.

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simplicity of this arrangement is rather rudely disturbed, when it appears that Porcellio has to be divided into seven genera or sub-genera and Oniscus into five, and in fact with one or two recent additions the Oniscidæ contain twentyone genera instead of only six. Little more can be done here than to mention their names.

Porcellio, Latreille, 1804. In this genus, after restriction, Budde-Lund describes seventy-one species, besides giving the names of more than a score recorded without description or imperfectly described. To this long list additions have since been made, as lamellatus, Uljanin, from the Mediterranean and the Azores; cristatus, Dollfus, from Surinam; Marioni, Aubert and Dollfus, from Marseilles; provincialis, Aubert and Dollfus, from Salon, in one of the districts of Provence, the most arid and remote from human habitations. Moreover, four or five new species from Syria, chiefly collected by Dr. Th. Barrois, have been named by M. Dollfus during the year 1892. Only the following four species out of this extensive genus have been recorded in Great Britain. 1.-Porcellio scaber, Latreille, is extremely common over the whole of northern and central Europe and the North of America. It extends to Greenland, and none of the land Isopoda range further to the north than this does. It is said also to reach the Cape of Good Hope and to have been found in Central America. 2.-Porcellio pictus, Brandt, is perhaps the same as the earlier Porcellio spinicornis, Say. It is distinguished by a large apical tooth on the second joint of the second antennæ, and by the black and yellow markings of the peræon. Together with the preceding species it belongs to a section of the genus in which the last segment is triangularly produced, with a sharp apex. 3.--Porcellio dilatatus, Brandt, belongs to a section in which the last segment is produced with a rounded apex. It does not appear to be at all common in Great Britain. 4.-Porcellio lævis, Latreille, belongs to a group distinguished from that which includes all the other three by having the hind margins of the first three peræon-segments less laterally sinuate, the sideplates less, with the hinder angles in the earlier segments

more obtuse, scarcely prolonged backwards, with the lateral process small, obtuse or none. All the four species agree with the species found in Syria in belonging to the division of the genus in which there are two pairs of tracheæ, as distinguished from another division in which there are five pairs. The extensive distribution of Porcellio laris is emphasised by Budde-Lund in the words 'Patria: Orbis terrarum.' It was obtained by the Challenger at Bermudas, the Cape Verde Isles, and at Honolulu. M. Adrien Dollfus observes that while Porcellio scaber is abundant in the cold and temperate regions both north and south, but not in the tropics, Porcellio lævis appears to have followed man all round the world except in the cold regions of the two hemispheres.

Cylisticus, Schnitzler, 1853, has the body more convex and contractile than it is in the preceding genus. The branchial-opercula of all five pairs of pleopods are furnished with trachea. Cylisticus convexus (De Geer) has priority over the name Porcellio armadilloides, Lereboullet, used in the British Sessile-eyed Crustacea.' Budde-Lund describes seven species of Cylisticus.

Hemilepistus, Budde-Lund, 1879, is notable for ample sculpture with spines or coarse granulation on the front part of the body, of which, however, the young ones are devoid. Budde-Lund describes ten species, all of which are found in the sandy deserts of Africa and Asia. One of them, Hemilepistus ruderalis (Pallas), was described by Pallas in 1771. The first and second pleopods, and more rarely the third or all are provided with trachea.

Metoponorthus, Budde-Lund, 1879, meaning 'with a straight front,' is frequently mis-spelt Metoponorthrus, to which no intelligible meaning could be assigned. BuddeLund gives descriptions of thirty-five species. In this genus is included Metoponorthus cingendus (Kinahan) found in the coast regions of England and Brittany, but distinct from the species so named by Budde-Lund from the highlands of the South of France, which Dollfus has therefore renamed Metoponorthus meridionalis. This has three pairs of trachea, whereas Kinahan's species has only

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