THE GENDERS OF GENERA

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The species Pseudocorystes armatus, Milne-Edwards, was found at Valparaiso, and Milne-Edwards supposes that it may be the same as the 'Grass Crab,' figured by Browne in his History of Jamaica,' pl. 48, fig. 2.

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Atelecyclus, Leach, 1813, is a member of the family in which the third maxillipeds, contrary to the family custom, do make a complete closure of the mouth-cavity. The type species, Atelecyclus septemdentatus (Montagu), was first observed on the south coast of Devon. Its carapace is nearly circular. Leach says that to the fishermen it is well known by the name of old man's face crab. The antero-lateral margin on each side is furnished with nine teeth, and probably for this reason Leach thought himself justified in changing the name to heterodon, in which he has been followed by Bell. Montagu perhaps did not think that the point at each extremity of the series ought to be counted in, and at any rate no one can be injured by the retention of the name which it was his privilege as the discoverer of the species to choose.

Thia, Leach, 1815, is represented both in the Mediterranean and in British waters, probably by one and the same species, called Thia polita by Leach in 1815, in allusion to the polished surface of the carapace, but as there is no substantial reason for thinking it distinct from the species described and figured by Herbst as Cancer residuus in 1799, its name ought to be Thia residuus (Herbst), although some may prefer to call it Thia residua, not reflecting that the animals are both male and female, and ignoring the old rule of Latin grammar that the masculine gender is to be preferred to the feminine. In this species, which like Corystes is a sand-burrower, the pleon is very narrow in both sexes, and, though in the male it is only five-jointed, the transverse grooves of the composite joint are so strongly marked, that all the seven joints. might at first glance be thought to be distinct, as they are in the female.

To conclude the discussion of the names used in this family, it may be mentioned, first, that although de Haan rightly claims priority for Dicera which he established

in 1833 over Nautilocorystes instituted by Milne-Edwards in 1837, yet Dicera must give way, having been already earlier used in other classes of zoology; and secondly, that Oēidia, de Haan, 1833, a name meaning egg-like, must likewise be cancelled, having been found to be a synonym of Gomeza, Gray, 1831, a Corystid genus of the Japanese fauna.

Legion 4.-Thelphusinea.

The carapace is more or less dilated at the branchial regions; the third maxillipeds have the fifth joint articulated at or near the front inner angle of the fourth or at its apex. The fingers of the walking legs are usually spinuliferous; the verges of the male pass directly through the basal joint of the fifth pair.

The species are fluviatile or live in damp forests.

Family Thelphusidæ.

This being the only family has the characters of the legion. Thelphusa, Latreille, 1819, contains numerous species, of which Mr. Miers observes that one, the common Thelphusa fluviatilis, occurs not only on the shores of the Mediterranean, but also in Asia Minor, Syria, and Persia; the others are found in all the warmer temperate and tropical regions of the old world, extending southward to the Cape of Good Hope, Madagascar, and Australia, but not to New Zealand; a species (Thelphusa chilensis) occurs in Chili.' Potamonautes, Macleay, and Geothelphusa, Stimpson, are so closely related to Thelphusa that their separation from it remains a matter of doubtful expedience.

Krauss remarks that the Thelphusida are especially fond of clear running streams in which they shelter themselves under stones and plants. They are easily scared, and in spite of their monstrous chelipeds their long peræopods carry them off at a great pace. The pearly Thelphusa (Thelphusa perlata, Milne-Edwards) has an earthy greenish colour, which matches its surroundings in the rivulets, whereas Thelphusa depressa, a species

which Krauss found at a waterfall in Natal, is yellowish and orange-coloured, in accordance with the cushions of moss among which it has its residence. Thelphusa dehaanii, White, occurs in the paddy fields of Japan, and has been taken at an elevation of 2,500 feet above the sealevel. It has been already mentioned that the river crab of Europe is good eating. Milne-Edwards supposes that it was to this crustacean that Aristotle referred under the name Carcinus Heracleoticus.

Paratelphusa, Milne-Edwards, 1855, was at first supposed to be a marine genus, but has since been proved to be an Indo-Malayan genus of fresh-water crabs, several species of which have been described by Mr. Wood-Mason. They differ from the rest of the Thelphusidae in having the distal end of the fourth joint of the chelipeds armed with a sharp spine, and are also said to have a greater general resemblance to some of the Cancridæ.

Dr. de Man, in his elaborate Report on the Podophthalmous Crustacea of the Mergui Archipelago ('Journ. Linn. Soc.' 1887, 1888), includes the genus Thelphusa in the next tribe, and the same arrangement is followed by Dr. Camil Heller in his Crustacea of the Novara,' 1865, the Thelphusinea being in fact intermediate in structure between the Cancrida and the Gecarcinidæ.

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CHAPTER VII

TRIBE II.-CATOMETOPA

THE front' is bent downward. The carapace is broad anteriorly, often subquadrate, sometimes subglobose, truncate or arcuate forwards, but not rostrate. The epistome is short, often almost linear. The pairs of branchiæ are usually fewer than nine in number; the efferent channels open at the sides of the endostome. The third maxillipeds have the fifth joint articulated at the front outer angle of the fourth, or less frequently at its apex, or very rarely at the front inner angle. The male verges are inserted either in the sternal plastron, or in the basal joints of the last pair of legs, thence passing through channels in the sternum beneath the pleon.

The tribe contains four families, the Gecarcinidæ, Ocypodidae, Grapsidæ, and Pinnotherida. The liver is said by Milne-Edwards to be in general central, extending little or not at all over the branchial cavities.

Family 1.-Gecarcinidae.

The carapace is dorsally very convex, especially dilated over and in front of the branchial regions, with the anterolateral margins usually entire and strongly arcuate. The front' is of moderate width and strongly deflexed. The orbits and eye-stalks are of moderate size. The third maxillipeds have the fifth joint articulated at the front outer or near the front inner angle or at the apex of the fourth, which sometimes completely conceals it. The chelipeds in the adult male are powerful, usually unequal. The seventh joint in the walking legs is nearly always

granulated and armed with longitudinal rows of spines. The pleon of the male usually covers the whole space between the bases of the last pair of walking legs.

These land-crabs are called Toulouroux by the French. They inhabit the warm territories of both hemispheres. The third maxillipeds suffice without other details to discriminate the genera.

Uca, Leach, 1817. The third maxillipeds have the fifth joint attached at the outer angle of the fourth; the inner edges of the third and fourth joints are in one line; along their outer edges the exopod is externally visible, and has a flagellum. Gecarcinucus, Milne-Edwards, 1842. The third maxilli

peds have the fifth joint attached to the middle of the apical margin of the fourth; the inner edges of the third and fourth joints are in one line; the exopod as in Uca. Cardisoma, Latreille, 1825. The third maxillipeds

have the fifth joint attached at the outer angle of the fourth; the inner edges of the third and fourth joints form a re-entering angle; the exopod as in Uca

Gecarcoidea, Milne-Edwards, 1837. The third maxillipeds have the fifth joint inserted in a deep groove of the apex of the fourth; the inner edges of the third and fourth form a re-entering angle; the exopod is without flagellum and concealed beneath the third joint.

Gecarcinus, Leach, 1815. The third maxillipeds have the fifth joint attached on the inner margin of the fourth and completely concealed by it; the inner edges of the third and fourth joints form a reentering angle; the exopod as in Gecarcoidea. Hylaocarcinus, Wood-Mason, 1874. The third maxillipeds have the fifth joint attached to the middle of the apex of the fourth; the inner edges of the third and fourth form a re-entering angle; the exopod as in Gecarcoidea.