If the tiny young of the Crustacea attack and destroy one another, it is not for want of innumerable other enemies fitted to keep their numbers in check. As far as the timidity of human experience can decide, the Crustacea in general, though by no means particular as to the food they consume, invite rapacity by the agreeable quality of the food they supply. The enormous spines of the very young and the strong armature of the adults have probably been called into existence in consequence. Where these are wanting or inadequate, the life of the species has been protected by extreme fertility. In Geryon quinquedens, Smith, for example, it has been computed that one specimen was carrying no less than forty-seven thousand eggs, and there are other species reckoned to be at least twice as prolific.

To the extensive genus Xantho Bell assigns three British species, naming them florida, rivulosa, and tuberculata. But, Montagu's floridus having lapsed as a synonym, the first of the three should be named Xantho incisus, Leach. The second, on Bell's own showing, ought to be called Xantho hydrophilus (Herbst), and of this Couch's tuberculata is now held to be a variety.

Ozius, Milne-Edwards, 1834, was a genus established to receive certain species found in the Indian and Australian waters. The name had been given much earlier by Dr. Leach, but without published description. It presents a peculiarity by help of which the large family of the Cancridæ is divided into two sections. The space between the front margin of the buccal frame and the mouth itself was called by Milne-Edwards the prelabial space. By English writers it is called the endostome or palate. In Cancer, Xantho, and many other genera, this endostome is without distinct longitudinal ridges defining the apertures of the efferent branchial channels, whereas in Ozius, Pilumnus, Eriphia, and others, it has these ridges.

Pseudozius, Dana, 1851, is, as the name implies, a genus that might be mistaken for Ozius, but the crests of the endostome do not quite reach the upper margin of the buccal frame. In 1881 the species Pseudozius Mellissi

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from St. Helena was carefully described by Mr. Miers, who pointed out its resemblance to and differences from Xantho Bouvieri, A. Milne-Edwards, a species from the Cape Verd Islands. In 1886 Mr. Miers re-described it, and gave a figure of it in his' Challenger Report,' but he then placed it in a new sub-genus Euryozius, entitling it Pseudozius bouvieri, var. mellissii,' in a hesitating manner identifying it with the species Xantho Bouvieri of A. Milne-Edwards. In 1888 Professor Th. Barrois, in his catalogue of the marine Crustacea of the Azores, once more describes this species, and gives a beautiful figure of it in its natural colour of bright orange-red, with black tips to the chelipeds. He and Mr. Miers are in exact agreement in their descriptions, as two such excellent naturalists were likely to be. But Professor Barrois calls the species Ozius Edwardsi, and explains that he had submitted it to the highly competent judgment of M. Alphonse Milne-Edwards, who pronounced it to be a new Ozius, of which he had himself obtained a specimen at the Canaries during the expedition of the Talisman. It will be consoling to the beginner and the amateur, when involved in perplexity amid species that they cannot name or can only name at random, to find the past masters of the science thus entangled as it were in their own web. For it must not be forgotten that Alphonse Milne-Edwards is acknowledged to be the highest authority on the Brachyura,' and yet he leads Barrois to make a new species of that which had been twice described and twice named by Miers, and which had probably been already named and described by Professor Milne-Edwards himself. The instance is significant of the stress, to which the highest powers must sometimes prove unequal, of keeping in mind each individual species of the vast multitude now known, and each individual chapter of the vast literature which records them.

Barrois mentions an interesting peculiarity in this elegant crab. The carapace along the antero-lateral margins is obliquely striated on the under side with fine parallel grooves, in correspondence with which the fifth joint or 'Miers, Challenger Report, p. 146.

wrist of the chelipeds has a long sharp crest, and the rapid rubbing of this crest against the striæ produces a shrill sort of stridulating noise such as a grasshopper makes by drawing the thighs of its hind legs over the salient nervures of its wing-cases.

Pilumnus, Leach, 1815, is represented in Great Britain by the single species Pilumnus hirtellus (Linn.), but for the world at large more than eighty forms have been described under separate specific names, and still await the discriminating criticism of some future monograph. In this genus, as at present defined, the antero-lateral margins are normally armed with spines instead of the usual teeth, and the pleon is seven-jointed in both sexes. But when the description and figures of Pilumnus xanthoides, Krauss, 1843, are examined, they exhibit not spines but rounded teeth or lobes on the antero-lateral border, and a five-jointed pleon in the male. Thus there is prima facie reason to suppose that this species ought to be removed to some other genus. Otherwise the boundaries of the existing genus must be enlarged, whereas for convenience they rather require to be narrowed.

Pirimela, Leach, 1815, like Pilumnus, is represented in Great Britain only by a single species, Pirimela denticulata (Montagu), which occurs also in the Mediterranean, but, unlike Pilumnus, it is not represented by any other species elsewhere. In this genus the pleon of the female is sevenjointed, but that of the male five-jointed, the three middle joints being coalesced into a single piece. It differs from all the rest of the Cyclometopa in the character of the third maxillipeds, for here the fourth joint receives the articulation of the fifth on its inner instead of on its apical margin.

Family 2.-Trapeziidæ.

'Carapace depressed and nearly quadrilateral, smooth, with the postero-lateral angles truncated, the dorsal regions not defined; the antero-lateral margins are straight, form a right angle with the front, and are entire or have but one tooth (the lateral epi-branchial tooth) developed.

The

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front is horizontal, broad, lamellate, and projects over the antennules and bases of the antennæ, which are widely excluded from the orbits.'

The genera are Trapezia, Latreille, 1825, Tetralia, Dana, 1851, and Quadrella, Dana, 1851, names indicative of the prevailing shape. The species in general are small and confined to the warm seas. According to the Russian writer, Paulson, 1875, the lower antennæ of Tetralia require that the last clause of the above-quoted definition should be cancelled.

Family 3.-Portunidae.

The carapace is depressed, moderately transverse, and usually widest at the last antero-lateral marginal spine. The front is horizontal and not spatuliform (see p. 71). The orbits and eye-stalks are of moderate length. The spine or tooth at the outer angle of the orbit does not project laterally beyond the teeth of the antero-lateral margin, of which more than one, usually from five to nine, are developed. The last legs of the trunk are commonly adapted for swimming, with the seventh joint ovate, flatly expanded.

The Portunidae include about half as many genera as the Cancridæ.

Carcinus, Leach, 1813, has the seventh joint of the fifth legs narrowly lanceolate. The species Carcinus mænas (Pennant) is the most obtrusive of all the British Brachyura. Its numbers justify its English designation as the Common Shore Crab; its extremely vivacious movements and its reckless audacity when brought to bay justify its scientific title and the corresponding French name for it of Crabe enragé. In the early part of this century Leach stated that it was sent to London in immense quantities and eaten by the poor. Professor Stalio says that at the present day it is a considerable source of food-supply to the humbler classes on the shores of the Adriatic, that in the soft state, just after the shedding of the skin, it is welcome at the tables of the rich, and that the Istrian fishermen pound it up and use it as a most attractive bait to the sardines. On

the other hand, complaints are made by English writers of the mischief which it does to fish already captured, and Dr. Hoek accuses it of the truly detestable crime of invading the oyster beds, and eating the young oysters while their shells are still soft and easy to break. In attacking the adults, it is itself sometimes caught by the snapping down of the powerfully hinged valves.

The only other species of this genus known is the American Curcinus granulatus (Say), and even this may not be really distinct from the European form.

Portunus, Fabricius, 1798, has the last two joints of the fifth legs dilated and compressed, and the last joint ovate. It is by this formation that many of the Portunidæ are qualified as swimming crabs. In the Caribbean Sea, and among the gulf weed in the tropical Atlantic, Mr. Gosse observed them shooting through the water almost like a fish, with the feet on the side that happens to be the front all tucked close up, and those on the oppo site side stretched away behind, so as to hold no water, as a seaman would say, and thus offer no impediment to the way.' Our British species swim with less facility, and are often called fiddler crabs, because, as Mr. Gosse explains, 'the see-saw motion of the bent and flattened joints of the oarfeet is so much like that of a fiddler's elbow.' The beautiful Velvet Crab, Portunus puber (Linn.), called in the Channel Islands the Lady Crab, is for ordinary purposes sufficiently described by Bell in the British Stalk-eyed Crustacea,' together with six other species of the genus that have been obtained in the waters of Great Britain, namely depurator (Linn.), corrugatus (Pennant), arcuatus and pusillus, Leach, holsatus, Fabricius, and its near ally marmoreus, Leach. To these Canon Norman has added Portunus tuberculatus, Roux, from the Shetland Isles. remarks on the singularity of the circumstance that this and many other southern forms should be found in the deep Shetland waters, though they are not known from localities between those waters and the Mediterranean.

He

Portumnus, Leach, 1814, both by name and structure, closely approaches the preceding genus, but it has the