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 CRUSTACEANS isopod Asellus aquations (Linn.), and for the freshwater amphipod Gam- mar us pule x (Linn.), Mr. John Hopkinson, editor of the 'transactions of the Hertfordshire Natural History Society, informs me by letter that he can personally vouch as belonging to the fauna of Hertfordshire. The Entomostraca of the county still await their chronicler. Mr. John Hopkinson has kindly supplied me with a reference to the above mentioned 'Transactions, vol. vii. p. xlix., which notes that a pond in Tittenhanger Park contains several species of Daphnia and Cyclops. Though there is no reason to distrust the information, it is rather vague. More important is the manuscript list with which Mr. Hopkinson has obliged me, containing the names of fifteen species of Entomostraca which he has himself observed in the neighbourhood of Watford, when studying pond life from twenty to twenty-five years ago. The list comprises the Phyllopod, Chirocephalus diaphanus ; the Clad6cera, Daphnia pulex, Daphnia vetula, Daphnia reticulata, Eurycereus lamellatus ; the Ostrac6da, Cypris tristriata, Cypris fusca, Cypris minuta, Candona reptans, Candona hispida ; and the Copepoda, Cyclops signatus, Cyclops tenuicornis, Cyclops serratulus, Canthocamptus minutus, and Diaptomus castor. Of these the most striking is undoubtedly Chirocephalus diaphanus, Prevost, which appears to be far more common than was at one time supposed. In regard to the other species, there has been of late years so much revision of nomenclature that few lists dating back a quarter of a century can be expected to correspond at all closely with the names now accepted. Sometimes also an older name has been found on more minute investigation to cover more than a single species. Thus Baird's Daphnia reticulata answers in part to Ceriodaphnia reticulata (Jurine), but in part to Ceriodaphnia megalops, Sars, and without fresh inquiry it is not possible to say which of the two is the Hertfordshire species. Very likely both occur in the county. Baird's Daphnia vetu/a is now called Simocephalus vetu/us (O. F. M tiller). 1 For the five species of Ostracoda respectively, the names preferred in Brady and Norman's recent mono- graph are Cypris -virens (Jurine), Cypris f us cata, Jurine, Cyclocypris Icevis (O. F. Miiller), Erpetocypris rep fans (Baird), and Cypris fuscata, Jurine. 2 From the last of these changes it will be perceived that, while one name may sometimes cover two species, in return two names may sometimes cover but one species. In the group of Copepoda, Cyclops tenuicornis, Lubbock, and in part Cyclops signatus, Brady, are both now made synonyms of Cyclops albidus, Jurine. 3 For Canthocamptus minutus the generic name should rather be Canthocampus. Cyclops fimbriatus, Fischer, is recorded by Dr. G. S. Brady, on the authority of Mr. Scourfield, from Stanstead, Herts. 4 Of the occurrence of parasitic Copepoda in Hertfordshire I find no express record, but in many instances their presence may safely be inferred 1 Scourfield, The Essex Naturalist, vol. x. pp. 314, 315 (1898). 3 Scourfield, The Essex Naturalist, vol. x. p. 325 (1898). 4 Nat. Hist. Trans. Northumberland, Durham, and Netvcastle-ufon-Tyne, vol. xi. p. 91. I8 7
 * Trans. Royal Dublin Soc., ser. 2, vol. iv. pp. 74, 73, 69 (compared with vol. v. p. 718), 84.