Page:VCH Staffordshire 1.djvu/165

 CRUSTACEANS Unlike most crustaceans, the Cladocera swim by means of the branching second antennae, to which the name of the group refers. Another comparatively uncommon feature, uncommon at least as affecting adult life, is the extreme transparency of the test or carapace which covers without concealing the details of the organism. There are two sections of the group, each divided into two subsections, but as it happens all the species as yet definitely recorded from this county belong to one and the same subsection. In the section Calyptomera, the feet and body of the animal are well covered by the carapace. In the subsection Anomopoda, instead of six pairs of feet all alike foliaceous, branchial, and non-prehensile, there are five or six pairs, of which the two anterior are more or less prehensile, not branchial and foliaceous, and differing from the hinder pairs. - This sub-section includes the majority of the Cladocera in general, and among them that which is most widely known, Daphnia pulex (de Geer). The familiarity which breeds contempt allows men to speak and write of this innocent crustacean as 'the water flea.' That either Mr. Garner or Mr. Brown observed the true D. pulex in this county, it is impossible to guarantee. Within the genus Daphne or Daphnia there are many species and varieties which only experts laboriously distinguish. That the family Daphniidae is here really represented may be trusted from the mention of Daphnia vetula (Straus) as the blunt- headed water flea. But this species dates back further than Straus to O. F. Muller, and at a later date became the type of Schodler's genus Simocephalus, so named because the head is obtuse at the top instead of keeled, as in Daphnia. The new generic name, however, was preoccupied, and has recently been changed by Dr. Norman to Simosa. Two other members of the same family have been found by Mr. Hodgson in Staffordshire, namely, Scapholeberis mucronata (O.F.M.) at Kingswood, and Moina rectirostris (Jurine) in a horsepond near Harborne. 18 The last genus is distinguished from the other three by not having a distinct rostrum, and by having the first antennae of the female long and freely mobile. In Daphnia the dorsal and ventral margins of the valves are drawn gradually together to end in a long or short process, which may be ventral, or inclining to dorsal, but which leaves nothing that can be clearly distinguished as a hind margin. In Scapholeberis, on the other hand, the straight or nearly straight ventral margins are produced into processes, the bases of which are connected with the dorsal edge by a clear stretch of hind margin. In Simosa the hind margin is large and rounded off at each extremity. Mr. Hodgson reports Ilyoeryptus sordidus (Lievin) from Kingswood. This mud-loving species belongs to the family Macrotrichidae, in which long and mobile first antennae are the rule, instead of the exception as in the case of Moina among the Daphniidae. The species with which we are here concerned is said to lead an unromantic existence, having given up the natural use of its second antennae as swimming organs, to employ them only for crawling over the mud or burrowing in it, usually in a considerable depth of water. Under the family Lynceidae Mr. Brown reports that several undetermined species of the genera Eurycercus and Chydorus are common in stagnant water. The statement is partially redeemed from indefiniteness by the circumstance that the former genus is, so far as known, represented in England only by a single species, Eurycercus lamellatus (O.F.M. ). Chydorus, it is true, has some four or five species recorded from the British Isles, but of these C. sphaericus (O.F.M.) is considered to be the commonest and most widely distributed of all the Cladocera, so that its occurrence here may be regarded as certain. Alonella nanus (Baird) was taken by Mr. Hodgson at Kingswood. For the family containing these three species the name Chydoridae should be adopted in place of Lynceidae, since the genus Lynceus has been shown to have its systematic place elsewhere. 19 A. nanus is said to be the smallest Entomostracan known at present. 20 It may well be called the dwarf, since the female is only just over and the male is just under one hundredth of an inch in length. Chydorus sphaericus, however, in the male sex is never much longer. But its female is sometimes twice as long, and this in turn is surpassed in sevenfold degree by the female of Eurycercus lamellatus. That species, therefore, exhibits a veritable giant measuring nearly a sixth of an inch from head to tail, and matching this length by a similarly unusual depth between the dorsal and ventral margins. Concerning the Ostracoda or box-entomostracans which, unlike the Cladocera, have no distinct head, but are shut up in their two valves like little molluscs authorities for this county supply no definite information. That species of the genera Cypris, Muller, and Candona, Baird, both belonging to the family Cyprididae, ' are abundant in ditches,' is a statement that would no doubt be applicable to all our counties. 18 Synopsis, p. in. " TheZool. (1902), p. 101.
 * Journ. Quekett Microsc. Club (ser. 2), vol. viii, p. 444 (1903).