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). 

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