CRUSTACEANS appendages are opercular, but the second pair, Asellus aquaticus (Linn.) by the judgement of Cocks and Bate is as common in the ponds and ditches of Cornwall as in those of other counties. The neighbouring family Janiridae consists of marine genera. Janlra maculosa, Leach, has a small scale or exopod on the second antennae. Bate says of it ' not infrequent on the coast. They have been taken at Falmouth, Polperro, and Plymouth.' * Cocks, using the name Oniscoda macu/esa, Latreille, reports it 'Under stones, algae, etc. : not uncommon.' The two little species Jaera albifrons, Leach, and J. nordmanni, Rathke, are both recorded by Bate from Plymouth, 2 and the former by Cocks from ' Gwyllyn-vase, Swanpool, etc. : not uncommon.' Its name according to Sars should be J. marina (O. Fabricius), and he is doubtful whether the English authors may not have mistaken the male of this species for Rathke's /. nordmanni. 3 The tribe of the Epicaridea, isopods parasitic upon other crustaceans, embraces a great number of peculiar forms. As yet only five of the genera have been, it seems, recorded from Cornwall, each in respect to a single species. All five belong to the family Bopyridae. For Athelgue paguri (Rathke), Bate and Westwood employ Rathke's name Pbryxus paguri, and say, ' We have received the male and female of this species from Polperro, collected by Mr. Couch.' 4 Pleurocrypta galateae, Hesse, is said by Giard and Bonnier to be the species which Bate and Westwood figure and describe as Phryxus longibranchiatus, remarking ' From Polperro we have received specimens of both sexes captured by Mr. Loughrin upon an old specimen of Galathea squamifera, of a much larger size than those represented above, the male being ^ in. and the female -}J in. long. 5 Bate in his ' Revision ' calls it Phryxus logibrachitus. lone thoracica (Montagu) is recorded by Cocks, who unpatriotically attributes the species to Latreille, as ' Found under the carapace of the Callianassa subterranea : not uncommon.' To most collectors this is a rare crustacean's rarer parasite. Bate and Westwood describe a species as Gyge hippolytes (Kroyer) from Ireland, adding, 'Another specimen (of the female), which appears to us to belong to the same species, and which has supplied the central figure in the above woodcut, was forwarded to us from Polperro by Mr. Loughrin.' 6 Its host is not mentioned. The genus should perhaps be Bopyroides (Stimpson). Bopyrus squillarum, Latreille, is recorded by Cocks as ' Found under the carapace of the Palaemon serratus : not uncommon.' For Palaemon should be read Leander. Bate calls this parasite ' Bopyrus squillariusj and says, ' Frequently found under the shell of prawns and shrimps. From Polperro and off the coast.' 7 Whether it is ever, not to say frequently, found on shrimps is extremely doubtful. The tribe Oniscidea comprises the terrestrial Isopoda commonly called woodlice. The Cornish list is evidently capable of development. In the family Ligiidae is the large shore-frequenting Ligia oceanica (Linn.), reported by Cocks as common, and in the Trichoniscidae the little Trichoniscus pusillus, Brandt, which Bate and Westwood record from ' Polperro (in the garden of the inn, not uncommon) ; Looe abundantly, among sticks by the riverside.' 8 In the Oniscidae, Cocks mentions Oniscus asei/us, Linn., Porcellio scaber, Latreille, and P. laevis, Latreille, all as common. Bate and West- wood add the two British species of Philoscia, the sylvan P. muscorum (Scopoli) and the beach-loving P. couchii, Kinahan, of which Bate says, ' It was discovered at Talland Cove, near Polperro, from whence we were returning accompanied by Professor Kinahan, who gives this account of its discovery : ' In returning home we took the clifF road, and at Talland Cove spent a few moments examining the supra-littoral zone (the tide being nearly full in). Here, as might be expected, Ligia oceanica, Porcellio scaber, Pbiloscia muscorum, and Orchestia llttorea were abundant ; but I was much pleased by also meeting with a Pbiloscia new to me, and also undescribed in the books. This I have named Philoscia Couchii, in memorial of one of the pioneers of the zoological geography of England, and of a few pleasant hours spent in his company. The species appeared abundant.' 9 Lastly in the family Armadillidiidae Armadillidium vulgare (Latreille) on the authority of Cocks and Bate is common and very abundant in Cornwall as elsewhere. In English science the Amphipoda had attracted little attention prior to the efforts of Mr. Spence Bate. The often-quoted work in which he and Westwood were partners was published in twenty-three parts between October, 1861, and December, 1868. Since then knowledge of the subject has greatly advanced, with the usual result that numerous changes of nomenclature have been introduced. The Amphipoda agree with the Isopoda in having the body tripartite, the cephalic portion ending with the maxillipeds, the peraeon or trunk comprising seven segments with their limbs, the pleon or tail usually well developed. But this last portion does not as in the Isopoda carry the breathing organs. Its first three segments are furnished with flexible pleopods, its next three with rigid uropods. The branchial vesicles connected with the limbs of the trunk are not enclosed in any chamber, and are generally simple. There are three well-marked divisions of this order, the Caprellidea, in which the pleon is degraded ; the Hyperiidea, in which the four 1 'Revision,' p. 66. s Ibid. p. 66. ' Crust, of Norway (1897), vol. ii, 104. * Brit. Sett. Crust, vol. ii, 242. 6 Ibid. vol. ii, 248. 6 Ibid. p. 231. 7 ' Revision,' p. 64. 8 Brit. Sets. Crust, vol. ii, 457. * Ibid. p. 453. 277
