THE MISCHIEVOUS GRIBBLE

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that the mandibles have no 'palp' or only a one-jointed one. By the antennal joints projecting in front, the uropods extended behind, and the large side-plates of the peræon radiating laterally and distally widened, the head, the back of the peræon, and the pleon are completely enclosed, and the outline becomes an unbroken oval. The animal, being only one-fifth of an inch long, might, like the still smaller Campecopea hirsuta, seem to be no fit subject for protective mimicry. It must be supposed that, minute as they are, they are found worth eating by creatures highly enough organised to be guided in their attacks by form and colour.

Family 6.-Limnoriidæ.

The body is sub-depressed; the pleon has six distinct segments. The eyes are lateral, wide apart; the antennæ of both pairs are short, the first having a single-jointed flagellum; the mandibles have a chisel-like cutting edge, the molar tubercle obsolete, the 'palp' small, three- (or perhaps sometimes two-) jointed; the first maxillæ have two slender plates, the second have three; in the maxillipeds the second joint is produced, the five joints of the 'palp' are short, its three middle ones somewhat expanded; the epipod is elongate; all the limbs of the peræon are similar, not prehensile, but with bifid fingers; the five pairs of branchial pleopods are sheltered in the vaulted pleon, all ciliated except the fifth pair, which is smaller than the rest; the second pair in the male have the usual stilets; the uropods have two single-jointed branches, both movable, the outer much shorter than the inner.

Limnoria, Leach, 1814, is the only genus. The type, Limnoria lignorum (J. Rathke, 1799), known at Plymouth as the Gribble, has an evil fame for gnawing submerged timber. It is widely distributed. Inaccuracies in the earlier descriptions of the species have been pointed out by the late Mr. Oscar Harger with his accustomed care and acuteness. In New Zealand Mr. C. Chilton has found a second species, Limnoria segnis, on the roots of the sea

weed Macrocystis, not burrowing into wood. He believes that the 'palp' of the mandible is only two-jointed. The epipod of the maxillipeds is much larger than in Limnoria lignorum, and is apically widened instead of having an acute apex.

A BOX OF BRANCHIE

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CHAPTER XXIII

TRIBE III.-VALVIFERA

HERE the uropods undergo a remarkable metamorphosis, and assume a function distinct from any that they have elsewhere, for like a pair of folding doors they form a great part of the ventral surface of the pleon, these valves closing over the five pairs of branchial pleopods or opening to admit the water to them.

6

In the History of the British Sessile-eyed Crustacea,' vol. ii. pp. 358, 368, 375, 378, the uropods are successively spoken of as 'the first or anterior pair of pleopoda,' as pertaining to 'the first segment of the tail,' as being absent in the Idoteida, where there is said to be a 'conversion of the fifth pair of pleopoda into a continuous operculum for the protection of the branchial organs,' and lastly, in the genus Idotea, as 'a strong outer pair (which are the terminal uropoda), forming an operculum' over the 'five pairs of very delicate branchial appendages.' Of these four statements the first two are consistent but erroneous, the last two are inconsistent with the first and with one another; only the final one is correct. All the four, as it happens, appeared in the same number of the work, namely, Part 19, published October 1, 1867, so that the confusion is difficult to account for, even as an accident of dual authorship.

The tribe includes two well-separated families, the Arcturida and Idoteidæ.

Family 1.-Arcturida.

The form of the animal is elongate and sometimes cylindrical; the segments of the pleon are more or less

B B

coalesced. The second antennæ are large and long; the mandibles have a molar tubercle but no 'palp;' the outer plate of the first maxillæ and the inner plate of the second are broad; the maxillipeds have an oval epipod, a broadly expanded plate to the second joint, and the five joints of the 'palp' not very large; the first four pairs of limbs of the peræon are directed forwards, slender, ciliated, with the terminal joint minute; the last three pairs are stouter, ambulatory, with the terminal joint bifid. The opercular uropods have the inner branch much shorter than the peduncle, the outer branch rudimentary or sometimes entirely wanting. When the valves are closed the branch of the uropods which is homologically the outer is shut up inside, even when present.

Arctūrus, Latreille, 1804, has the flagellum of the second antennæ more than four-jointed, the fourth segment of the person not greatly longer than the others, the marsupium of the female composed of four pairs of plates. The arctic Arcturus Baffini (Sabine) grows to a length of three inches. Mr. F. E. Beddard has described thirteen new species brought from various parts of the world by the Challenger. Others have been described by Miers, Sars, and Studer. Almost all have a striking appearance from the armature of spines or tubercles. In their clinging habit and general appearance they have some resemblance to the amphipod group, the Caprellida, some of which are also very spinose. It is interesting to observe that in creatures which are structurally very distinct a similar mode of life goes with a similar general appearance, so that the similarity of life may be supposed to have produced the similarity of look.

Astacilla, Cordiner, 1795 (=Leacia, Johnston, 1825), has the flagellum of the second antennæ not more than fourjointed, the fourth segment of the peræon much longer than any of the others, and the marsupium of the female consisting of two plates affixed to this segment. There is no reason for discarding Johnston's Leacia, on the ground that the different name Leachia was preoccupied. It is a common and quite justifiable practice to form generic names

CORDINER'S LITTLE LOBSTER

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variations on the same theme, as Darwinia and Darwinella. Harger points out that Fleming's reference of Astacilla to the Rev. Charles Cordiner, 1784, is no proof that it was published or described at that date. But in a work entitled Remarkable Ruins and Romantic Prospects of North Britain with Ancient Monuments and Singular Subjects of Natural History by the Rev. Charles Cordiner of Banff. London, 1795,' there is a section headed 'Astacillæ, Purple Doris, &c.,' containing the interesting passage which follows:—

'One very lively species of little lobsters, which had taken up their dwelling among these coralines, seemed on account of its novelty to merit the attention of a particular drawing.

'Their general form and appearance in their natural state, and the size of life, are carefully represented at a, a, a; an elaborate delineation of the microscope, after a minute investigation of the particular structure of its several parts, is inserted above at A. That will more distinctly express to the curious the peculiarities of the animal than any specific distinctions which could be narrated. The eye appeared as a regular arrangement of bright specks, in circular rows, as at the figure I.

The diminutive ASTACILLE, of the general name of lobsters, is applied at present, as a common characteristic, until one more particularly appropriate may be fixed on to distinguish it by; for these are a species that do not appear to have been yet recognized among the varieties of British insects.'

Seeing that this account is accompanied by an unmistakable figure of Astacilla longicornis (Sowerby), it seems only proper to uphold the priority of Cordiner's generic name, and perhaps the name of the family ought to become Astacillida. The British species are Astacilla longicornis (Sowerby), Astacilla intermedia (Goodsir), Astacilla gracilis (Goodsir), Astacilla damnoniensis, Stebbing, Astacilla Deshayesii (Lucas), and Astacilla dilatata, Sars. This last and others of the genus named by the same author are found on the coasts of Norway. Astacilla granulata, Sars,