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 CRUSTACEANS saying of this that it is ' equally common with the last and in similar situations, under stones about low-water mark.' According to Bell this is probably the form mentioned by Leach as a variety of the preceding species, with claws coloured like the carapace. Bell adds that ' Mr. Couch of Polperro was the first to detect it as an English species, and to refer it to its proper name.' * Couch called it Zantho rivulosus, with a reference to Milne-Edwards. Bell declares it to be undoubtedly the Cancer hydrophilus of Herbst, so that he gives Couch credit for naming it properly just after showing that his naming was wrong in every particular. The distinction between the two species is not especially obvious : X. hydrophilus has a flatter carapace, with the antero-lateral teeth much less obtuse, the fingers of the great claws brown instead of black, the movable finger grooved instead of plain, and the ambulatory legs more continuously hairy. Cocks records both from localities near Falmouth. A third species was subsequently introduced to science by Mr. R. Q. Couch, who described examples of it taken from near the Runnel-stone in Mount's Bay, in the crevices of Eschara foliacea? He says in a footnote, ' A specimen has been submitted to Professor T. Bell of King's College, London, and he has pronounced it a new species, and has assigned to it the name Xantho Couchii.' Bell, in the appendix to his work on the British Stalk-eyed Crustacea, describes it as Xantho tuberculata, R. Q. Couch, m.s., and declares that ' the name of tuberculata has been given to the species by its discoverer." 3 This name refers to the tuberculation of the great claws or cheu'f <"ds, which is a distinguishing feature of this little species. Bate 4 affirms that this species ' was first described by Mr. Bell in his book on the British Crustacea.' But as it only appears in the appendix to Bell's volume, which was completed in 1853, there cannot be a doubt that Xantho couchii, Couch, is the earlier and so far the valid name, although the two authors by their reciprocal politeness have confused the matter as much as they well could, with the result that R. Q. Couch may easily be misrepresented as having had the vanity to name his discovery after himself. There has been an inclination to regard this third species as a variety of X. hydrophilus, but the eminent French naturalist E. L. Bouvier has vindicated its independence, 6 and in fact transferred it to another genus, for in a joint work on the Decapoda of the Talisman and Travailleur Expeditions he and his colleague, the late Alphonse Milne-Edwards, say of this species, ' one of us has recently pointed out its essential character, and shown that it ought rather to be ranked under Xanthodes than under Xantho.' 6 Why they continue to place it in a genus in which they admit that it had better not be placed is left unexplained. Xanthodes is no doubt not very distinct from Xantho, but it has the inter-orbital border more instead of less than half the greatest width of the carapace. If both genera are accepted, the species under discussion must now be known as Xanthodes coucbii (Couch). The extensive and wide-ranging genus Pilumnus (Leach) is here represented only by the little P. hirtellus (Linn.) called the ' Furry Pilumnus ' by Couch, who found it ' common under stones at low-water mark,' 7 just as Cocks at Falmouth found it ' between the layers of shelving rocks, under stones, Gwyllyn-vase, Swanpool, etc. ; common.' 8 The carapace is distinguished from that of Xantho by its hairiness and the sharpness of its antero-lateral teeth. The pleon or tail has in both sexes seven distinct segments, whereas in the male Xantho the third, fourth, and fifth are fused into one. Pilumnoides perlatus (Poeppig) has been sent me from Falmouth by Mr. Vallentin, who found it on a derelict vessel which had been towed into that famous harbour. Whether such an immigrant can rightly be counted in the Cornish fauna may be open to question, but beyond doubt it is an interesting example of the manifold ways in which the distribution of species may be effected. P. perlatus is far less pubescent than Pilumnus hirtellus, and in place of sharp teeth it has the antero- lateral margins subdivided into four unequal granular lobes, from the hindmost of which a slightly concave ridge extends obliquely backward on the carapace. The Portunidae or swimming crabs furnish many species to this and other parts of England. Several of them belong to the genus Portunus (Fabricius), and of these all that are known to be English have also been recorded from Cornwall. The largest is P. puber (Linn.), called in France the Woolly crab, more elegantly in England the Velvet crab, from the pubescence on its carapace and limbs. This velvety coat is beautifully slashed by bare spaces of a vivid blue. Couch says : 1 Brit. Stalk-eyed Crustacea, p. 56. 1 Rep. of the Penzance Nat. Hist, and Antiq. Sue. for 1851, p. 13. Couch's paper stands between others specially dated 1851, the inference being that these essays were published at intervals during that year, although the Report 'for 1851 ' containing the whole collection would naturally not be issued till 1852. 3 Brit. Stalk-eyed Crustacea (1853), p. 359. 4 ' Revision,' p. 10. 5 La Feuille dei Jeunei Naturalistes, ser. 3, No. 332 (1898). * Op. cit. (1900), p. 94. 7 Fauna, p. 70. from internal evidence obviously cannot have been published till 1850. The 'Contributions to the Fauna of Falmouth,' by Mr. W. P. Cocks, will be frequently quoted. It will be convenient to abbreviate the reference to Cornwall ' Soc. (1850). 1 257 33
 * The largest keep in water of the depth of a few fathoms, and the smaller about low- water mark,
 * The Seventeenth Ann. Rep. Roy. Cornvi. Polyt. Sac. (1849), p. 79. The report, though dated 1849,