Page:VCH Warwickshire 1.djvu/220

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A HISTORY OF WARWICKSHIRE names. In particular the species L. quadrangularis was transferred in 1843 by Dr. Baird to a new genus, Alona. Baird indulged in the incon- sistency of retaining the family Lynceidas, although he left in it no genus Lynceus. Mr. Hodgson and some other authorities have avoided this fault by retaining the genus Lynceus in place of Alona. But Lynceus cannot be in two places at once. Being a phyllopod, it cannot likewise be a cladoceran. For several of the genera in this family Baird notices something distinctive in the external form. Thus, Cbydorus, Leach, is ' nearly spherical in shape ' ; Acroperus, Baird, ' somewhat harp-shaped ' ; Alona, ' quadrangular' ; Eurycercus, Baird, ' sub-quadrangular' ; Camp- tocerus, Baird, and Peracantha, Baird, respectively 'ovoid' and 'oval'; while Pleuroxus, Baird, has the lower part of the ventral margin ' trun- cated, or, as it were, cut sharp and straight.' He contrasts the motion through the water of Alona quadrangularis with that of the Daphniidae, for ' instead of swimming by short irregular bounds, as these latter do, they direct themselves by a rapid motion of their inferior antennae, or rami, and legs, straight towards the point to which they wish to go.' ' He considers that this probably depends on the shortness of the branches of the second antennas, since among the species of another family Bosmina longirostris, which also has very short branches similarly situ- ated, has the same kind of motion. As in the Daphniidas, so in the Chydoridas, the eye, Baird observes, ' is a spherical body contained in a somewhat funnel-shaped sheath of muscles, having a semi-rotatory motion, and consisting of a series of crystalline bodies, which, in the Eurycercus lamellatus, are about twenty in number.' 2 In Eurycercus Dr. Jules Richard notes that the optic ganglia and their nerves are clearly separated one from the other, though all the same the eye remains single, 3 thus strengthening the recognized probability that the single eye of the Cladocera has arisen from the fusion of eyes originally paired. Passing on to the Gymnomera, we find this section likewise divided into two tribes, the Onychopoda with four pairs of feet, nail-bearing feet as the name implies, and the Haplopoda, with six pairs of feet, these being in accord with the name simple, unarmed. The so-called nails of the Onychopoda are supplied by unguiform setae. In this tribe the family Polyphemidas supplies Warwickshire with the interesting species Polyphemus pediculus, de Geer. Mr. Hodgson describes its distribution as ' local : Olton Mill Pool ; Blackroot, Sutton.' In the second tribe the family Leptodoridas supplies Leptodora hyalina, Lilljeborg, ' abundant, canals and some large pools.' This species was recorded in 1879 from ' a pool in the neighbourhood of Olton ' 4 by Mr. Walter Graham, F.R.M.S., President of the Birmingham Natural History and Micro- scopical Society, his identification of it being corroborated by Professor Ray Lankester. Lilljeborg now accepts L. kindtii (Focke) as its right name. 1 British Entomostraca, p. 122. * Loc. cit. p. 117.

  • Ann. Set. Nat. ser. 7, vol. xviii. p. 312. * The Midland NaturaSst, ii. p. 225, pi. 5 (1879).