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 



