Page:VCH Warwickshire 1.djvu/216

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A HISTORY OF WARWICKSHIRE a series of twenty or more simple or isolated denticles. Diaphanosoma brachyurum (Lievin) has a very different appearance, owing to the enor- mous size of its second antennas. In Mr. Hodgson's list it appears as Daphnella brachyura^ LieVin, but the name Daphnella being preoccupied has had to be relinquished ; and possibly our British species ought to be known as Diaphanosoma wingii (Baird), a question of names that might prove extremely profitable to lawyers if a title and estates depended on the decision. The second tribe is called Anomopoda, to signify that the feet are not all alike, the two front pairs being, in contrast to those of the Cteno- poda, more or less prehensile, not foliaceous. This tribe, which comprises most of the Cladocera, is divided into four families Daphniidas, Bosmi- nidas, Macrotrichidae and Chydoridae each taking its name from the eldest of the genera it contains. In the first three of these families the second antennas have the dorsal branch four-jointed, the ventral three- jointed ; but in the fourth family both branches are three-jointed. In the first family the intestinal canal has in front two coecal appendages, but forms no loop ; in the second, it has neither loop nor coeca ; in the third, it is variable, being generally without the cceca, and sometimes straight, sometimes convoluted ; in the fourth, it forms almost a double convolution. Not in every kind of animal, nor yet in every kind of crustacean, does the shape of the intestine offer an easy guide towards the distinction of families. But with most of the Cladocera the chitinous envelope is so pellucid, sometimes of such a glassy transparence, that the course of the alimentary tract can be perfectly perceived from the out- side, without any necessity for killing and dissecting the specimen. In the Daphniidae Mr. Hodgson records Daphnia fu/ex, de Geer, 'abundant in dirty water'; D. longispina, Miiller, 'abundant in clear water, canals'; D. lacustris, var. ga/eata, G. O. Sars, 'common: Olton, Whitacre, Sutton'; D. jardtnii, Baird, 'common: Olton, Whitacre, Sutton'; with var. kahlbergensis, Schodler, 'Olton,' and var. cederstromii, Schodler, 'Blackroot, Sutton.' In regard to the first of these species, Dr. G. S. Brady, F.R.S., in a paper 'On the British species of Ento- mostraca belonging to Daphnia and other allied genera,' under the head- ing, 'var. brevispina (Daday de Dees),' writes as follows: 'Mr. D. J. Scourfield has sent to me specimens taken in the neighbourhood of Birmingham, which are different in some respects from the ordinary form of D. pulex, and I think are the same as those described by Daday de Dees under the specific name bre-vispina. They do not however appear to me to require more than a varietal name. The spine is rather longer than that which I look upon as belonging to the typical D. pulex, and the principal abdominal processes are short, curved, nearly equal in length and divergent, the whole animal of a deep brown colour.' * Daph- nia longispina is a small species, taking its name from the great length of the spine at the extremity of its test. It labours under two disadvan- tages. No one is quite sure what species O. F. Miiller was really 1 Nat. Hist. Tram. Northumberland, etc. vol. xiii. pt. 2, p. 223 (1898). I 7 8