A HISTORY OF ESSEX 



ephippium.' * Subsequently however he found that although this 

 structure in the Chydorus might be regarded as the most highly evolved 

 of the proto-ephippia hitherto recorded, an advance upon it was made 

 in no less than three respects by the homologous structure in Leydigia 

 acanthocercoides, of which he says : ' First, it is formed, as in the 

 Daphnidae, from a much more limited portion of the shell, bounded 

 approximately by a semicircle described upon the dorsal margin ; 

 secondly, it possesses a thick inner coat of specially formed spongy 

 tissue ; and thirdly, it is provided with large hook-like appendages. In 

 spite of these advances in complexity however it does not quite reach 

 the level of the Daphnidan ephippium, because its outer coat is not 

 specially altered beyond the mere deposit of pigment and some extra 

 chitin perhaps, whereas in typical ephippia there is always a more or 

 less abundant development of closely-set hexagonal prismatic cells which 

 are quite independent of the original cell structure, and which, becoming 

 readily filled with air, render the ephippium lighter than water.' 



Of the Ostracoda all but one in Mr. Scourfield's list belong to the 

 family Cypridids, in which the valves are usually smooth and the hinge 

 not toothed. They are Cypria exsculpta (Fischer) ; C. ophthalmica 

 (Jurine) ; Cyclocypris serena (Koch) ; C. /avis (O. F. Miiller) ; Cypris 

 fuscata, Jurine ; C. incongruens (Ramdohr) ; C. virens, Jurine, a large 

 species which ' is essentially an inhabitant of very small pieces of water, 

 especially such as are well stocked with aquatic vegetation ' ; C. (?) 

 reticu/ata, Zaddach ; ' C. tessellata (in part), Brady [1868] : only the 

 immature " tessellata " forms from Wanstead Park have hitherto been 

 seen, so that it is still a little uncertain whether they should be referred 

 to C. reticulata or not ' ; C. obliqua, Brady ; Erpetocypris reptans (Baird) ; 

 E. strigata (O. F. Miiller) ; E. tumefacta (Brady and Robertson), this and 

 the two preceding species belonging properly to Erpetocypris as instituted 

 in 1889, not to Herpetocypris as proposed in 1896, the name in either 

 form alluding to the creeping habit, as to which Norman and Brady 

 write : ' The power of swimming is lost, and the habits of the animals, 

 which creep along the bottom, are thus very different from those of 

 Cypris ' ; 2 Prionocypris serrata, Norman ; Cypridopsis vi//osa (Jurine) ; 

 Pionocypris vidua (O. F. Miiller) ; Notodromas monacha (O. F. Miiller) ; 

 Ilyocypris gibba (Ramdohr) ; Candona candiaa (O. F. Miiller) ; C. /actea, 

 Baird ; C. compressa (Koch) ; C, pubescent (Koch) ; C.fabceformis (Fischer). 

 In regard to C. pubescens the remark is made that ' within the Epping 

 Forest area it has only been found at Wanstead Park, and this is in fact 

 its only known British locality, as the reference to Pavenham [Bedford- 

 shire] in Brady and Norman's Monograph [part z] p. 729 was made 

 under a misunderstanding.' The name of the genus Notodromas, Lillje- 

 borg, signifies a dorsal runner. Of animals that can move easily with 

 the back downwards house-flies on our ceilings are familiar examples. 

 Many kinds of Entomostraca swim by preference on their backs. In 



1 The Annual of Microicopy, p. 64 (Oct. 1898). 

 * Trans. Royal Dublin Soc. ser. 2, vol. iv. p. 84 (1889). 

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