A HISTORY OF BUCKINGHAMSHIRE 



ler, and Acroperus harpce, Baird, both procured in Stoke Park, and be- 

 longing to the genera with the head keeled on the top, are distin- 

 guished one from the other by the tail of the female. This in the 

 former genus is long and slender and armed with spines on the hinder 

 or upper margin, but in the latter is ' of moderate length and breadth, 

 without spines on the aforesaid margin, and only furnished on the sides 

 with uniform fascicles of very minute spines.' * No very large bowl is 

 needed for constructing a miniature pond in which to observe the man- 

 ners and customs of these creatures. Their modes of motion are very 

 various, and familiarity with these may be utilized for determining the 

 kinds present in an aquarium. Mr. Scourfield says : ' Of all the 

 peculiar modes of existence, that ef deliberately making use of the 

 ceiling of a pond, i.e. the surface-film of water, for support, is probably 

 the most remarkable. So far as is known, only a very few species have 

 acquired the power in a fully developed fashion, and these are all in- 

 cluded in two genera, namely Scapholeberis (Cladocera) and Notodromas 

 (Ostracoda).' In regard to S. mucronata he explains that on the per- 

 fectly straight and flattened ventral margin of each valve there exists a 

 series of very peculiarly modified setae, the anterior and posterior mem- 

 bers of which are larger and project somewhat more than the rest ; 

 when the animal, which habitually swims in a reversed position, brings 

 its ventral margin into contact with the surface of the water, the setas 

 which project farthest from the shell pierce the surface-film and pro- 

 duce minute capillary depressions. 8 These depressions, it appears, are 

 large enough to support the difference in weight between the animal's 

 body and the water which it displaces. By careful observation and ex- 

 periment Mr. Scourfield has also determined that in addition to the 

 morphological distinctions there is also a fundamental difference in the 

 swimming habits of Dapbnia and Ceriodaphnia on the one hand, and 

 Simosa and Scapholeberis on the other, for whereas the two former always 

 swim either vertically, or obliquely back uppermost, the two latter al- 

 ways swim more or less obliquely back downwards. 3 Of Cbydorus 

 sphcericus Baird observes that its motion through the water is more like 

 rolling, as Jurine describes it, than swimming. 4 



Of the Ostracoda, so abundant everywhere both in species and in- 

 dividuals, there is for the moment only a single Buckinghamshire record, 

 the common Cypris fuscata, Jurine, having been taken in a pond on a 

 common near Burnham Beeches. 



Of the Copepoda there are five species included in three genera, 

 a small collection but covering rather a wide space in classification. 

 Diaptomus castor (Jurine) occurred together with the Ostracode just men- 

 tioned. It belongs to the extensive family of the Diaptomidas, which is 

 comprised in the division of the Copepoda called by Giesbrecht Gym- 

 noplea. To explain this expression, it must be pointed out that in this 

 order of animals the body is theoretically divisible into eleven segments, 



> Cladocera Suecite, p. 400. 2 >uekett Microscopical Club, p. 309 (1900). 



> Loc. cit. p. 395 (Nov. 1900). * British Entomostraca, p. 127. 



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