CRUSTACEANS respect to a limited number of these, among which Notodromas monacba is included, Mr. Scourfield has pointed out an interesting special adapt- ation. To several of the minute Crustacea the surface-film of water proves a dangerous trap. When accidentally placed upon it they are disabled from effecting a return by their own exertions to its underside. But by help of a flattened ventral area, water-repellent surfaces and film- piercing ridges, Notodromas monacba turns the risky situation to its own advantage. ' Close attention to the movements of an isolated specimen will show that although it swims nearly vertically, the moment it touches the surface it assumes a horizontal position, back downwards, thus bringing its straight ventral margin into close contact with the surface-film. ... In this position the animal may continue to move about for an indefinite period, usually rather briskly, but sometimes so leisurely that no doubt is left in the observer's mind that the weight of its body is actually supported by the surface-film.' For further details and the philosophy of the matter whether as a question of physics or as affecting the safety of the animal and its chances of food supply, the "Journal of the Linnean Society should be consulted. 1 The ostracode that remains to be mentioned is Limnicythere inopinata (Baird). This belongs to the family Cytherida?, which is almost exclu- sively marine, among the few exceptions being the species of Limnicythere. Of L. inopinata Brady and Norman say that it is ' generally distributed in ditches, lakes and slowly running streams throughout the British Islands ; found also not uncommonly in estuarine localities, and sometimes dredged at sea, though in these cases it has probably been washed down out of fresh water.' 1 The Copepoda of Essex are distributed among three families. One of these is called Calanidae by Dr. G. S. Brady in 1891, but more recent classification allots that name to a different set of species. Accordingly Mr. Scourfield follows the high authority of Giesbrecht and Schmeil in using the name Centropagidas, but it is clear that the family ought to take its name from the earliest genus within it, and therefore it will properly be called the Diaptomida? from Diaptomus, Westwood, 1836. This genus gives to Essex D. castor (Jurine), a large species ' practically confined to small weedy pools, such as occur plentifully on Leyton Flats ' ; D. graci/is, Sars ; D. vu/garis, Schmeil, * one of the commonest of the genus on the continent, or at any rate in Germany,' not hitherto known as British except from 'The Lake,' Wanstead Park, though probably not really uncommon, ' as it is more than likely that this form has been mistaken for D. graci/is, to which it is very closely allied ' ; Eurytemora lacinulata (Fischer), of which the usual habitat 'is in brackish pools near the coast : as a freshwater animal it is decidedly rare,' Mr. Scourfield only knowing of four British freshwater localities for it. The question of its range appears to be rather complicated by an intricate synonymy. 1 Journ. Linn. Soc. Lentlon, vol. xzv. p. 10 (1896).
- Trani. Royal Dub. Soc. ser. 2, vol. iv. p. 170 (1889).
1 217 28
