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CRUSTACEANS describing under this specific name, and that which is now allowed to carry the title is so variable that not only have many nominal species been carved out of it and then discarded, but it is almost impossible by words to fix its characters. They change with the individual, with the locality, with the season, with the conditions of nourishment, with the sizes and ages even of ovigerous adults. 1 D. jardinii, Baird, is now usually transferred to the genus Hyalodaphnia, Schodler, distinguished from Dapb- nia by the want of an eye-spot. Brady, in 1898, perhaps overlooking Mr. Hodgson's record, declares that the only British locality in which H. jardinii has hitherto been found is Lochmaben, Dumfriesshire. 2 On the other hand he accepts H. kablbergensis [kahlbergiensis], 3 Schodler, as an independent species. In the same way he does not hold galeata to be a variety of D. /acustris, but describes it as D. galeata, Sars ; and further on he says, 'The characters, which may be taken as separating D. kablber- gensis from D. galeata, are the large size of the head, its wedge-shaped outline, broad at the base or posterior end and gradually tapering to an acute apex, and the absence of an eye-spot : the vertex-spine, which in D. galeata has a ventral bend, is here either straight or slightly bent to- wards the dorsum.' 4 Under D. galeata he had already observed that ' in other respects a description of the one form may very well be applied to both.' 6 In 1879 Mr. H. E. Forrest described and figured ' D. Bairdii' from Olton reservoir. He says, 'The appearance of D. Bairdii in the microscope is irresistibly comic. It has an immense head, which terminates upwards in a sharp point, exactly as if it were wearing a dunce's cap, and in this its one goggle eye rolls about with an air of supernatural wisdom. The body is transparent and almost colourless.' 6 Subsequently Mr. Forrest explains that his D. Bairdii had been previ- ously found near Berlin, and described by Schodler as Hyalodaphnia kahl- bergensis, but he maintains that its name ought to be Daphnia kablbergen- sis, and in addition to Olton Reservoir gives as localities for it Edgbaston Pool and Spurrier's Pool. 7 Sars however in 1890 makes it a variety of Hyalodaphnia jar dinii (Baird), grouping together several so-called species, and explaining that 'the spring generations of this species usually have the head quite evenly rounded, without a hint of the more or less strongly outdrawn hood-shaped extension which characterizes summer genera- tions, and therefore exhibit a very different physiognomy, so much the more as also the eye seems considerably larger.' 8 There remains to be considered the var. cederstromii. For the species described by Schodler as H. cederstromii Dr. Jules Richard adopts the designation 'H. cristata, Sars ; var. cederstromii, Schodler,' stating that the variety is scarcely dis- tinguished except by the extraordinary development and the form of the 1 Richard, Ann. Set. Nat., ser. 8, ii. 277 (1896) ; and Lilljeborg, Cladocera Sued*, p. 95 (1900). 8 Nat. Hist. Trans. Northumberland, etc. vol. xiii. pt. 2, p. 238. 3 The name as given by Schfidler is kahlbergiensis, although, as will be seen, it is repeatedly quoted as kahlbergensis. 4 Loc. cit. p. 239. 6 Loc. cit. p. 235. 6 Midland Naturalist, ii. 217, pi. 14 (1879). 7 Loc. cit. p. 284. 8 Oversigt afNorges Crustaceer, in Chris tiania yid.-Selsk. Forhandlinger, No. I, p. 34. 179