CRUSTACEANS writer the following quotations may also be made, because from the presence of the fishes which he names may be inferred the existence in Herefordshire waters of the crustacean parasites with which those fishes are wont to be infested. He says that ' salmons were formerly sold at one penny per pound in Hereford, but now bring sixpence to half a crown, according to the time, and other circumstances.' ° ' Other sea-fish occasionally taken in the Wye, are shad, flounders, lamperns, and lampreys ; but none of these are met with frequently or in great abundance.' ' Besides these, the Wye has the usual kinds of river-fish, including pike, grayling, trout, perch, eels and gudgeons.' * It is well known that the salmon arriving from the sea brings with it a different kind of parasite from that with which it descends a river when returning seaward. The two species, however unlike in appearance, never- theless belong to the same order, the Copepoda. Since migration into fresh water relieves the salmon from its marine encumbrance, Lepeophtheirus salmonis (Kroyer), and a return to salt water drives off the Lernaeopoda salmonea (Linn.) which attacks it in the river, one may wonder whether these aquatic exchanges were originally induced by the pinpricks of the little crustaceans. There are no statistics available to tell us whether the parasites are becoming more euryhaline — that is, capable like the salmon itself of enduring wide differences in the salinity of the water they inhabit. If Duncomb, for instance, had been able to tell us that the Lepeophtheirus was never found on the salmon beyond the limits of brackish water, and the modern fisherman could affirm that it was now often found in water absolutely fresh, a suspicion would be justified that the entomostracan was extending its capacity for migration to match that of its host. Shads, like salmon, pass from the sea up rivers for spawning. In the fresh water they are said to improve in flavour. With regard to the AUis Shad, Alosa vulgaris^ Yarrell, Couch remarks that it is very uncommon to find them so far up as Worcester.' The Twait Shad, A. jinta (Cuvier), he says, is taken in the Severn at the same time with the Allis.'" From the gills of this latter species Mr, Bassett-Smith records the copepod Anchorella emarginata, Kroyer." Concerning the flounder, Pleuronectes fiesus, Linn., Couch observes that 'fresh water seems at times to have a particular charm for it, as it occasionally wanders upward in the deeper rivers to a considerable distance, and there it assumes a new appearance as regards colour, as well as that it is said to suffer loss in the quality of its flesh, but it seems doubtful whether it ever breeds in freshwater.' ^' The Pleuronectidae are apt to be infested by some species of the copepod genus Chondr acanthus, De la Roche. It would be interesting to ascertain whether the flounder carries such parasites with it into fresh water, and by so doing either causes them to quit their hold or to perish. Among river fishes the persecuting pike, Esox lucius, Linn., is itself exposed to the attacks of the parasitic Copepoda Ergasilus sieboldii, Nordmann, and Caligus lacustris, Steenstrup and Liitken. The latter is said also to frequent the less formidable perch, Perca fluviatilis, Linn., and this fish is subject to the visitation of two other species of the same group, Lernaeocera cyprinacea, Linn., and Achtheres percarum, Nordmann." ' Op. cit. vol. i (1804), p. 161. 'Ibid. 163. 'Ibid. 164. ' Hist. Brit. Fishes, iv, 1 26 (i 865). " Ibid. 122. "Prof. Zool. Soc. London, 1899, p. 503. " H»;/. Brit. Fishes, iii, 195 (1864). "Ibid. (1899), pp. 443,448,480,498. I "3 15
