The first five segments of the pleon are distinct, carrying each a pair of pleopods; the sixth segment ends in a pointed telson and bears inserted at the sides of the base a pair of two-branched uropods resembling the pleopods except in being of a firmer texture.

In the adult male the so-called mandibles are powerful and exserted beyond the front of the quadrate head; the maxillipeds have a palp' consisting of four flattened ciliated joints. The first segment of the peræon is separated from the head only by a suture, and its appendages, the first gnathopods, are (in Gnathia) two-jointed, opercular, the first joint being a large pyriform plate fringed with setæ on the convex inner margin and containing three semitransparent calcareous plates, supposed to indicate the same number of original joints. The seventh segment of the peræon is abruptly narrower than the preceding, so that it seems to form part of the narrow pleon. The pleopods with their two one-jointed rami are sometimes ciliated, and sometimes not. Dr. Dohrn considers that the so-called mandibles of the adult male are structures that arise independently of the true mandibles as found in the young. He considers that these new structures are not concerned in feeding, but only in attaching the animal to some object. For feeding purposes he states that the opercular gnathopods are thrown open, and the maxillipeds act as whirling organs, the current of water so maintained bringing with it small nutritious particles such as do not require any powerful oral apparatus for their mastication.

In the adult female the head is subtriangular, with the eyes (when present) larger and placed further back than in the male; the mandibles are said to be wholly lost; the maxillipeds are reduced. The first gnathopods with the joints unexpanded or not much expanded lie each on a delicate membranous plate which may be marsupial. The first and last segments of the peræon and the pleon are as in the male, but the fourth, fifth, and often the sixth segments of the peræon are fused, the dilated transparent skin affording a view of the young ones within.

When the young are ready to escape, the cuticle of the mother, previously separated from the hypodermis, splits into scales on the various segments.

In the young the mouth-organs project beyond the head, and are evidently formed for piercing and for suction; the mandibles have stiliform ends, and are followed by two pairs of slender organs, which are considered to be the two pairs of maxilla; the maxillipeds are also slender and elongate; and the first gnathopods are elongate, limb-like, with the normal seven segments; the first peræon-segment is distinct, the fourth, fifth, and sixth being perhaps fused in the young female and distinct in the young male. Dr. Dohrn considers it inappropriate to speak of the mandibles as without 'palp;' rather, he says, it is only the 'palp' which appears to be present.

It is said to be easy to keep the males alive for a year or two in a small bowl containing some of their native mud and some sea-water. As they are active climbers, precautions must be taken against their escape.

Gnathia, Leach, 1814, has long been the only genus contained in the family, to which it is entitled to give its name, as hinted by Bate and Westwood, and properly decided by the late Mr. Oscar Harger. For a long time the name Anceus, Risso, 1816, was used for the males, and Praniza, Latreille (Leach MS.), for the females and young. M. Eugène Hesse has the credit of having definitely established the relationship between the two forms, but it should not be forgotten that Leach had expressed his conviction of it as long ago as 1814. The female had already been figured and described as a marine Oniscus by Slabber in 1769. The best known British species is Gnathia maxillaris (Montagu) 1804. The 'mandibles' of the male distinguish it from the species Gnathia Halidaii (Bate and Westwood), instituted by those authors in 1866 with an expression of some doubt as to whether it might not be the same as Gnathia formica (Hesse). The American species, Gnathia cerina (Stimpson) may likewise be distinguished by the mandibles.' M. Hesse has described seventeen species from the coast of France, and given draw

ings of many of them that excite some surprise by the vividness of the colouring. His Gnathia asciaferus has 'man

dibles' of unusual shape, their axe-like appearance being alluded to in the specific name.

Gnathia

stygius (Sars) is more than half an inch long.

Euneognathia may be instituted as a new genus to receive the species Anceus gigas, Beddard, from Kerguelen. It is strikingly distinguished from Gnathia by having the first gnathopods in the male six-jointed. The pleopods have both branches fringed with long plumose hairs. The male of Euneognathia gigas (see Plate XIV.) exceeds three-fifths of an inch in length, and is therefore the largest known member of the family. The fourth and fifth segments of the peræon are markedly the widest.

FIG. 30.-Gnathia asciaferus (Hesse), the male [Hesse].

Anceus bathybius, Beddard, dredged from a depth of 900 fathoms, will no doubt require to be transferred to another new genus, but the species, being founded on a fragment of a specimen, may wait for a new generic name till fuller material is obtained.

Anceus Danielii, Hesse, 1884, may also represent a distinct genus, and probably, whenever the family is monographed, it will develop as plentiful a harvest of genera as its neighbours.