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 : 

 * The largest keep in water of the depth of a few fathoms, and the smaller about low- water mark, 



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. 



* The Seventeenth Ann. Rep. Roy. Cornvi. Polyt. Sac. (1849), p. 79. The report, though dated 1849, 

 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). 



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