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). 



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