CRUSTACEANS U. leucopis (Kr.), Bate and Westwood,' 5-5 mm. long, as taken in 10 to 20 fathoms, also off Southport. Pariambus typicus (Kroyer), formerly called by a pre-occupied name Podalirius, is reported as occurring throughout Liverpool Bay on the common starfish Asterias rubens} The Amphipoda, as at present known, are divided into three principal groups — Gammaridea, CapreUidea, Hyperiidea. The first group is by far the largest, and almost certainly that from which the other two have branched off. The third group is not represented in our list, but no doubt members of it are sometimes to be found, floating about or cast on the shore, domiciled in those ' Blebs,' or jelly-fishes, of which Dr. Leigh long ago took notice. Of the CapreUidea an example has just been mentioned in the little Pariambus, a fifth of an inch long, and very slender, with the fifth pair of legs degraded, and the pleon almost obsolete. This poor development of the tail part is characteristic of the whole group, and easily explained by the habits of the various species. It is all the more notable by contrast with this part of the body in the other two groups, where for different reasons the pleon is, as a rule, particularly conspicuous and important. Whether the whales which Dr. Leigh has recorded brought with them to Lancashire any of their parasites, the Cyamidas, is matter for conjecture. These little companions of the whale belong to the same tribe CapreUidea, and show a remarkable agree- ment with the skeleton-shrimps of the companion family Caprellidae, except in the one particular that they are much more substantially built. The Entomostraca of Lancashire, although as yet far from exhaustively investigated, offer already a rather large number of species, in regard to which some brevity of treatment must be excused. An outline of the general classification shows three orders — the Branchiopoda with branchial feet, the Ostracoda, shut up in sheU-valves, the Copepoda with rowing feet. Some, however, of the Branchiopoda have shell-valves like the Ostracoda, while some are entirely without them. Some use their feet for rowing like the Copepoda, but others have locomotive antenna5. One division, the Bran- chiura, has been as it were tossed to and fro between the Branchiopoda and the Copepoda, and, according to yet a third opinion, should be allowed an independent position between them. For the student bent upon sorting his specimens correctly these facts may seem unpleasantly perplexing, but they help to teach us that groups in some respects strangely dissimilar are never- theless closely united by bonds of relationship. To the order or sub-order Branchiura there belongs in England only the little greenish, almost circular, fish parasite Argulus foliaceus (Linn.), in which one pair of maxillae are trans- formed from jaws into suckers. Mr. Andrew Scott records it ' on trout from the Ribble, which were sent to University CoUege, Liverpool, for examina- tion.'* It makes its meals on various freshwater fishes and even on tadpoles. Mr. Charles Branch Wilson observes as to species in the United States of America that ' ordinarily the Argulidas roam about so freely as to occasion little discomfort to their hosts. They change frequently from one fish to another, and must of necessity desert their hosts at the breeding seasons, since their eggs are deposited upon some convenient surface at or near the bottom, and are not carried about with them. Any fish, therefore, no matter how badly it may be infested, has a chance three times a year to get comparatively 1 Op. cit. p. 313. ^ Op. cit. XV. 348 (1901). 167
