CRUSTACEANS 



Portunus Dalyellii, from a specimen obtained in Oxwich Bay, near Swansea. The lateral spines are 

 very largely developed in the figure given by Mr. Bate, but not more so than in many Mediterranean 

 specimens, and scarcely more than in Roux's figure. It is at a glance distinguished from all other 

 species [of Portunus] by the character from which the name has been given, namely, the length and 

 slenderness of the legs.' l White records it from ' off Falmouth in deep water ' on A. M. Norman's 

 authority. 2 Bate in 1878 rather reluctantly accepts the identification of his South Wales specimen 

 with the Mediterranean species found in Cornwall. In 1885 it was transferred by the late 

 Victor Carus to the genus Bathynectes, which signifies a deep swimmer. This was instituted by 

 Stimpson in 1871, and is distinguished from Portunus by having no median frontal tooth and by 

 having the lowest of the five antero-lateral teeth much more strongly produced than the others. 

 Bate describes the colour as ' a brilliant reddish brown with darker blotches of the same.' 3 



Polybius henslowii, Leach, is distinguished from our other Portunidae by its nearly orbicular 

 carapace and by the fact that its second, third, and fourth pairs of limbs share to some extent 

 in the compressed character of the terminal joints by which the fifth legs are converted into an 

 admirable pair of paddles. On the habits of this ' Nipper crab ' or ' Henslow's swimming crab,' 

 Jonathan Couch's observations have been quoted in full by Bell and by Bate. Its pertinacity in 

 Stacking fish and its skill in swimming have been amply confirmed by other observers. Cocks 

 report: it ' From stomach of the Gadus morrhua, G. aeglefinus, Trigla lyra ; not common. ' 4 The 

 Rev. Alfred Norman informed Adam White that he had ' seen the sandy beach between Hayle and 

 St. Ives quite strewn with the exuviae of this crab.' Mr. Edward Step has obliged me with a 

 specimen from Portscatho. 



Under the name Platyonichus latipes, or ' Widefoot,' Couch introduces the species called by Leach 

 Portumnus variegatus. Using the latter name Cocks reports it from ' Gwyllyn-vase Bay, Swanpool, 

 Mainporth, etc. ; rare. Hayle, St. Ives Bay, and stomach of fishes ; not uncommon.' No doubt it 

 ought to be called Portumnus latipes (Pennant). But the name is unfortunate. Portumnus is so like 

 Portunus that Latreille thought himself (though he was not) justified in changing it into Platyonichus. 

 Couch was content to rest the generic definition on the wide and oval termination of the hind legs, 

 in contrast to the ' corresponding part of the other legs straight and unfit for swimming.' Bate is 

 either ironical or too urbane when he says that ' This definition of Couch's is scarcely sufficient to 

 determine the genus from that of Portunus.'' 5 It is of course absolutely insufficient, seeing that both 

 genera share these very characters. Bell took up the genus with the amended spelling Platyonychus 

 for some of the species assigned to it by Milne-Edwards, but discriminated it from Portumnus, for 

 which it was originally only an alternative name. By some accident he attributed to Portumnus the 

 broad oval, very much rounded, terminal joint of the fifth legs, which in spite of the name latipes its 

 single species does not possess. 6 The joint in question is acutely lanceolate, and only moderately 

 widened. Bate says : ' Portumnus is easily detected by the form of the carapace, which is lyre-shaped, 

 and is as long as it is broad.' The antero-lateral teeth are very small. Leach says that the species, 

 ' when alive, is of a yellowish-white colour, mottled with purplish brown.' 7 



To Carcinus maenas (Linn.), the common shore crab, carcinology is under considerable obliga- 

 tions. Appreciation is sometimes won by rarity, sometimes by modesty, sometimes by delicacy of 

 structure or monstrous size. But in this case it is abundance, effrontery, hardihood, and handiness 

 that have been valued. On all our shores this crab is at everyone's disposal. It is beginning to 

 colonize Australia. 8 Nothing scares it. It will change its skin in a finger glass. It will breed 

 easily in captivity. It was especially serviceable to J. Vaughan Thompson, who crowned the researches 

 of many years by his memoir in the Transactions of the Royal Society (1835) on the 'Double Meta- 

 morphoses of the Decapod Crustaceans, exemplified in Cancer Maenas' On the Zoeaand Megalopa 

 stages of this same crab Mr. R. Q. Couch began the careful experiments and observations which he 

 extended to the young of numerous other crustaceans. His papers on this subject give special 

 distinction to the early Report of the Royal Cornwall Polytechnic Society. 9 His results amply confirmed 

 those of Vaughan Thompson, against which untenable objections had been raised by some naturalists 

 otherwise deservedly of the highest authority. Cocks, while stating that the shore crab occurs in 



1 Brit. Stalk-eyed Crustacea, p. 362. ' Popular History, p. 50. 



3 Ann. Nat. Hist. (1851), ser. 2, vii, 321 For distinction of this species from B. superbus (Costa) see 

 Norman in Ann. Nat. Hist. (1891), ser. 6, vii, 272. 



4 Without giving repeated references to Mr. Cocks's 'Contributions' in the Cornwall Soc. (1850), it may 

 suffice to say once for all that the quotations in regard to the Malacostraca are taken from pages 7884. 



5 'Revision,' p. 14. 6 Brit. Stalk-eyed Crustacea, p. 83. 



7 Edinburgh Encyclopaedia (1813), vii, 391. 



8 See Fulton and Grant in Proc. Roy. Soc. Victoria (1902), p. 55. 



s Cornw. Soc. (1844), Eleventh Annual Rep. p. 28, and (1845) Twelfth Annual Rep. p. 17, 'On the 

 Metamorphosis of the Crustaceans, including the Decapoda, Entomostraca, and Pycnogonidae.' For the most 

 recent criticism of Thompson and Couch, see Dr. H. C. Williamson's important paper on the shore crab in the 

 Twenty-first Ann. Rep. Fishery Board for Scotland, p. iii, 136 (1903). 



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