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 A HISTORY OF LEICESTERSHIRE swimming with regular, sometimes tolerably rapid movements, back upwards, repeatedly striking out behind with the hind-body. 86 It is probably to the latter action that it owes its generic name, which Baird explains as meaning flexible-tailed." It occurs only in Mr. Garnar's list, and Acroperus harpae, Baird, only in Mr. Scourfields. The oblique striation or ribbing of the valves in the latter species suggested the comparison with a harp. The generic name signifying a pointed extremity does not seem especially appro- priate, as the body is in profile more or less ovate, or even sometimes sub- rectangular. Alona, Sars, which takes the place of the pre-occupied Lynceus, is represented in Mr. Garnar's list by A, tenuicaudis ^ Sars, and A. rostrata (Koch), in Mr. Scourfield's by A, affinis (Leydig), A. guttata, Sars, and A. rectangula, Sars. The characters used by Lilljeborg for distinguishing these species show that A. rostrata has only seven swimming setae on the second antennae, while the other species have eight. Its specific name alludes to the length and acuteness of the rostrum in the female. In that sex the squamiform fascicles of fine spinules at the sides of the tail are well developed, and the last of them overtopping the caudal margin in A. rect- angula, but they are wanting or rudimentary and not overtopping the margin in the other three species. The hind or upper margin of the female tail is more or less angled in A. guttata, but rounded in A. affinis and A. tenuicaudis. Finally, in A. affinis the terminal spines of the upper caudal margin are about equal to those which precede them, but in A, tenuicaudis a few at the end are much larger than the preceding. A. affinis was first recorded as British by Mr. Scourfield in 1895, and the special marks distinguishing it from A. quadr angular is (O.F.M.) will be found given by him in detail on that occasion. 87 Leydigia quadr angular is (Leydig), first described by the celebrated zoologist after whom its present genus is named, has features, the interest of which is not diminished by the fact that some of them are common to all of the few species at present comprised in the genus. There are five pairs of feet, of which the fifth is the largest. The intestine forms almost a double loop. The eye-spot, instead of being as usual much smaller than the eye, is here considerably larger. This species belongs to Mr. Garnar's list. The next two are from Mr. Scourfield's. Alone lla nanus (Baird), being little over a hundredth of an inch or "2.6 mm. in length, may set up some claim to be a champion dwarf among the Cladocera, in accord with its specific name attached to a diminutive generic title. Small as it is, its residence is said to be by preference in large pieces of water. Peracantha truncata (O.F.M.) is named to suit the character of its valves which have a truncate hind margin beset with spines. It is unnecessary to follow Lilljeborg in the refinement of scholarship which leads him to lengthen the generic name into Peratacantha. Two species are entered by Mr. Garnar as Lynceus uncinatus and Lynceus denticulatus. Mr. Scourfield points out that the former should more properly be called Pleuroxus uncinatus, Baird, and as to the latter says, ' It is very unlikely that Mr. Garnar had Pleuroxus denticulatus ; P. denticulatus is too close to P. trigonellus and P. aduncus, to allow us to accept this identification without further evidence.' He subsequently wrote repeating his doubt as to this one species in Mr. Garnar's list, but adding, 'It is a British species, however, M Cladocera Sueciae, 409. M Brit. Ent. (Ray Soc.), 128. 17 Journ. Quekett Uicrosc. Club (Ser. 2), vi, 1 29. 104