Hemiarthrus abdominalis (Kröyer), 1840, on Hippolyte Gaimardii, Milne-Edwards. Kröyer states that he also found it on Hippolyte Sowerbei and another nearly related species. J. Sp. Schneider assigns it also to Kröyer's Hippolyte turgida and pusiola, and to Pandalus Montagui, Leach. Bate and Westwood speak of it as a parasite both of the Pandalus and of a species of Hippolyte. The full-grown female is of remarkable appearance, from her want of symmetry, her great marsupial plates enclosing a vast number of eggs, and the condition of her limbs, which form on one side a little crowded row, while on the other all have disappeared except the first. Hippolyte Sowerbei or rather Sowerbai, Leach, is a synonym of Spirontocaris spinus (Sowerby), and stands therefore in the genus to which the species pusiola and Gaimardii have also been recently transferred (see pages 235, 236).

Phyllodurus, Stimpson, 1857, is thus described by Stimpson, in Latin which if not pedantically classical, has at least the merit of being very easy for English readers to follow :-'Femina pedes thoracis sat validi, toti ancorales, unguiculati; appendicibus branchiales carentes. Appendices abdominis branchiales; superiores laterales, laminis duabus æquis magnis elongatis; inferiores papilliformes. Abdominis segmentus primus setis dorsalibus unguiculatis instructus.'

Phyllodurus abdominalis, Stimpson, 1857, from between the abdominal feet of the common Upogebia, Puget Sound. On the position of this species the recent authorities do not appear to express any opinion. The other Epicarids of Upogebia, Ione and Pseudione, are referred to the branchial cavity.

At the conclusion of this long catalogue it may be allowable to express a hope that its utility to the student will be in some measure proportionate to the time and trouble expended on producing it. It would have been easy to sacrifice the useful to the ornamental, and instead of showing the extent of the subject, to dwell only on the singularities, indulging in a disquisition on the extremely eccentric and abnormal forms included in this

THE SUBJECT NOT EXHAUSTED

419

group. With attention directed to the number of species actually existing, it is probable that the half-score described by Bate and Westwood as belonging to the British fauna will soon prove to be but the nucleus of a far larger company. By accepting the view that no parasite has more. than one species of host, we may greatly simplify the otherwise bewildering task of naming specimens, and so far leave the mind at leisure to grapple with the other numerous and intricate difficulties connected with this little-known tribe.

CHAPTER XXVII

TRIBE VII.-ONISCOIDEA

THIS tribe consists of the land Isopods, adapted for breathing air, but probably in all cases requiring that the air should be humid. In general uniformity and regularity of shape they are strikingly contrasted with the preceding parasitic tribe. The head is small, the seven segments of the peræon are distinct, the pleon is narrower, and usually has six distinct segments, of which the sixth is the smallest. The first antennæ never have more than three joints, and may have fewer, or may be wholly wanting. The mandibles are without palp.' The inner plate of the first maxillæ bears either two or three plumose setæ. The second maxillæ have two plates or only one. The maxillipeds are occasionally seven-jointed, but seldom more than four-jointed. The seven pairs of trunk-feet are similar to one another; the hinder more or less exceeding in length those that precede; all are gressorial. The pleopods are branchial. Of the five pairs rarely the first is obsolete; the second and sometimes also the first have sexual organs in the male. The uropods are of variable character, never powerful organs; their branches are single-jointed. Five families are included in the tribe, the Ligiidæ, Tylidæ, Helleriidæ, Oniscidæ, and Armadillididæ.

Family 1.-Ingiidæ.

The pleon consists of six segments, of which the first two are narrower than the third. The first antennæ are small, three-jointed. The first maxillæ have three setæ on the inner plate. The second maxillæ have two plates.

In the five pairs of pleopods the outer branch is opercular, the inner branchial, but sexual in the first two pairs of the male. The uropods are produced beyond the apex of the pleon. The young are said to quit the mother with only six pairs of trunk-feet. The family contains seven or eight genera.

Ligia, Fabricius, 1798, has a multiarticulate flagellum to the second antennæ, the maxillipeds with a small rounded epipod, and the 'palp' four- to five-jointed. The uropods have two equal, stiliform, often filiform, branches. Ligia oceanica (Linn.) is found on rocky shores of Great Britain and in many parts of northern and western Europe. The uropods are not unlike those of Asellus aquaticus. It attains a length of more than an inch, without including uropods and antenna. In Ligia exotica, Roux, the second antennæ are longer than the animal, the flagellum having from twenty-seven to forty-one joints. Ligia cursor, Dana, from Valparaiso, hints by its specific name at what is rather a character of the genus, rapidity of running. Von Siebold says that in Japan on rocky shores at ebb-tide in summer the Ligia are sometimes so abundant that the fishermen sweep them with brooms into pots, to be used for bait. Budde-Lund in 1885 describes in all twelve species from the shores of various parts of the world, and gives the names of five others. Ligia dilatata, Perty, he renames in 1879, Stymphālus dilatatus, and he includes Dana's Styloniscus, with its three species, in this family.

Ligidium, Brandt, 1833, has a multiarticulate flagellum. to the second antennæ, the 'palp' of the maxillipeds conical, five-jointed, the stem of the uropods obliquely produced on the inner side, and the inner branch tipped with two hairs. Five species have been described. Ligidium hypnorum (Cuvier, 1792) has had several names. In England it has hitherto only been recorded from the borders of Surrey and Sussex. Budde-Lund supposes that the Bavarian species Zia paludicola, Koch, and Zia melanocephala, Koch, belong to this genus.

Trichoniscus, Brandt, 1833, has the flagellum of the

second antennæ from two- to seven-jointed, the 'palp' of the maxillipeds obscurely two- to three-jointed, the branches of the uropods subequal or the inner thinner and rather shorter than the outer. Trichoniscus pusillus, Brandt, is identified with the British Philougria riparia (Koch), Trichoniscus vividus, Koch, with the British Philougria vivida, and Trichoniscus roseus, Koch, with the Philougria rosea, which not only occurs in many parts of England and other European countries, but has been taken by Mr. Chilton in New Zealand. The first two are little agile brown species; the third is especially attractive by its delicate rose colour, a tint so unusual in this tribe. Budde-Lund describes two other species, and names four more, one of the latter being the Scyphacella arenicola, S. I. Smith, of the United States. Dollfus describes four new species, two being from the Azores, one from Tristan da Cunha, and one from Valparaiso.

Haplophthalmus, Schöbl, 1860, has the flagellum of the second antennæ three-jointed, the legs shorter than in Trichoniscus, and the pleon less abruptly narrower than the peræon. The last character it shares with Smith's Scyphacella. The two species are Haplophthalmus Mengi (Zaddach), and Haplophthalmus danicus, Budde-Lund, both of them white.

Oligoniscus, Dollfus, 1890, is distinguished from Trichoniscus, because, the head being bent forward, the frontal line encroaches on the facial region, and because the eyes are simple. The specific name of the type-species, Oligoniscus monocellatus, from Juan Fernandez, corresponds in meaning with Haplophthalmus, the name of the preceding genus, from which it seems but little remote.

Titanethes, Schiödte, 1849, has no eyes, the flagellum of the second antennæ multiarticulate, the 'palp' of the maxillipeds three-jointed, the uropods with conical, stiliform, unequal branches. Titanethes albus (Koch) is the type. Five other species have been recorded. The genus appears to be confined to caverns.