flattened and ciliated. The incubatory pouch in the female is generally under the first four segments of the person.

The swimming joints above described resemble those found on some of the swimming crabs, and differ strikingly from what is customary among the Isopoda. To this family, indeed, the title of equal-legged animals is singularly inappropriate.

Munnopsis, Michael Sars, 1861, has the body suddenly constricted and slender behind the fourth peræon-segment. The second antennæ are very elongate, with the peduncle six-jointed. The mandibles are acuminate, with a secondary plate on the left, but not on the right mandible, without molar, and with a three-jointed 'palp.' The first and second limbs of the peræon are short, rather robust, subprehensile, the two following pairs enormously elongated; the three following pairs are natatory, without a seventh joint. The arrangement of the pleopods corresponds with that already described in Janira. The uropods are slender, single-branched. Munnopsis typica, Michael Sars, the typespecies, has a very extended boreal distribution in deep water on muddy ground. Hansen says that in the second antennæ the long fourth and fifth joints of the peduncle are immovably fused. In these organs the flagellum is nearly as long as the peduncle, and the two together are about five times the length of the body. By the great elongation of the fifth and sixth joints in the third and fourth limbs these equal about three times the body's length. Munnopsis australis, Beddard, with no 'palp' to the mandibles, and with the marsupium arising apparently only from one segment of the peræon, must probably be referred to a separate genus.

Eurycope, Sars, 1864, has the body not abruptly constricted. The second antennæ are very elongate, with sixjointed peduncle. The mandibles have a spine-row, molar, and three-jointed 'palp,' but no secondary plate on either mandible. The first pair of limbs are rather short, the next three pairs are long, and the last three pairs are natatory, with an unguiform seventh joint. The pleopods are as in the preceding genus. The uropods are short,

THE MUNNOPSIDE

385

two-branched, the branches single-jointed. Eight Norwegian species have been described by G. O. Sars, in some of which the second, third,

and fourth limbs are extremely elongate, but in Eurycope robusta, Harger, from the Gulf of St. Lawrence, they are not much longer than the body. The three species first described, Eurycope cornuta, phalangium, and mutica, all of Sars, range in length between a seventh and a sixteenth of an inch. Eurycope gigantea, Sars, extensively distributed in the high north, attains a length of an inch and a third, by a breadth of over half an inch. It is notable that this species and Munnopsis typica appear invariably to occur together. Both sexes are known of both. The first antennæ are shorter in the females than in the males. In Eurycope gigantea there is, according to Hansen, a little triangular plate on the third joint of the second antennæ, which may

re

be garded as a rudimentary exopod. It would not seem very rash to conclude from this that the first two joints are really one joint subdivided. The fourth

and fifth joints are, Hansen says, in this species firmly fused. Of the swimming-feet he observes that the feathered setæ are attached a little within the margin, to obtain support when displayed for swimming, and to have a resting-place when folded away between the strokes. Eight new species are named and described by Beddard from the Challenger explorations, all from considerable and some from very great depths.

Ilyarachna, Sars, 1869, 'mud-spider,' was named in place of the preoccupied Mesostěnus, Sars, 1864, meaning 'narrow in the middle.' The body is suboval, but deeply incised behind the fourth segment of the peræon. The second antennæ are long; the mandibles have a molar tubercle, and either have a small three-jointed' palp' or are without one. The first limbs of the peræon are not elongate, the second usually more robust than the rest, the third and fourth in general very elongate, the fifth and sixth natatory, with an unguiform seventh joint, the seventh long and slender, with the joints scarcely flattened, the nail long and curved. The uropods are simple, lying close to the pleon. Sars has described five Norwegian species, of which the first was Ilyarachna longicornis. Ilyarachna quadrispinosa, Beddard, was brought by the Challenger from Kerguelen.

Desmosoma, Sars, 1864, a chain-like body,' has the segments marked off by constrictions which are commonly deep; the three hinder segments of the pleon are larger than those which precede. The second antennæ are shorter than the body, slender in the female, robust in the male. The mandibles have a dentate cutting-edge, spine-row, molar, and usually a three-jointed 'palp,' ending in a long unguiform spine. The first four pairs of limbs are short and robust, the last three natatory, but with the fifth and sixth joints not greatly expanded, edged with spines that are flattened but not plumose; the seventh joint is narrow and stiliform. The uropods are simple, two-jointed, the last joint being the larger. Sars has described four Norwegian species, Desmosoma lineare, armatum, aculeatum, and tenuimănum, of which aculeatum has no mandibular ' palp.'

Acanthocope, Beddard, 1885, has the side-plates of the peræon, except the first pair, furnished with long spinelike processes, and the pleon ending in an elongate spinelike process. The mandibles have a powerful molar and a small, three-jointed 'palp.' The hind limbs of the peræon have a natatory character. The uropods are simple, long, and stiliform, from three- to five-jointed. In Acanthocope spinicauda, taken from a depth of 1,800 fathoms in the Southern Ocean, the five-jointed uropods present a feature unique in this tribe. Acanthocope acutispina, from South America, has three-jointed uropods, and the first antennæ with a short flagellum instead of a very long one as in the companion species.

CHAPTER XXV

TRIBE V.-PHREATOICIDEA

Family Phreatoicidæ.

Phreatoicus, Chilton, 1882. The only genus.

The animal is long, subcylindrical, laterally coinpressed. The seven segments of the peræon are distinct, with small distinct side-plates. The pleon has six distinct segments, the first five laterally produced downwards, the fifth longer than any of the preceding four, the sixth dorsally fused with the telson, but distinguished from it by lateral sutures or setose ridges. The eyes are small and lateral or absent. The first antennæ are short, the flagellum subterminally thickened and carrying olfactory filaments; the second antennæ have a five-jointed peduncle and a flagellum exceeding it in length. The mandibles have a dentate cutting edge, accessory plate on the left mandible only, a long spine-row, strong molar, and threejointed 'palp;' the lower lip is bilobed; these and the other mouth-organs agree in all important respects with those of Asellus, only that in the maxillipeds the fourth joint is strongly produced on the outer side. The first limbs of the peræon are subchelate, of the 'gnathopod' form. The rest are ambulatory, the last three pairs facing those in front as in most of the Gammaridea. All the pleopods have the outer branch ciliated, the inner and smaller branchial; the first pair have narrow branches; the second have in the male the usual stilets, which are curved and semicylindical, and the outer branch both in this and the following pairs is two-jointed. The uropods