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 CRUSTACEANS with Mr. Tomalin, for he says: ' In fact, I have observed that the well- fed Argulus can spend many days or even weeks separated from its host without nourishment.' ' Our next species belongs to a far more important division of the Branchiopoda, namely, those which from their divided or biramous second antenna are called the C/addcera, or ' branching-horns.' These include many families, numerous genera, abundance of species, and of individuals innumerable millions. Though this part of the population of North- amptonshire would defy the efforts of any census, it has attracted so little attention that I can only find a single record of a single species. This belongs to the family Sidida, which comprises seven genera. The genus Sida, Straus, from which the family name is derived, has indeed only one species, Sida crystallina (O. F. Miiller). But, to make up for this paucity, you may go from Northamptonshire to Nantes and to Norway, you may visit Berne and Berlin, you may travel to Moscow, to Shanghai, to Lake Superior, and at all these places, in small reservoirs, on the margins of ponds or in large lakes, meet with this little oblong trans- parent species, passing- through the water with ' a sort of rapid running movement,' or afSxed to water-weeds by an adhesive apparatus at the back of its head. Dr. Baird mentions among the places at which it has been taken in our islands, ' Back fish-pond at Overstone Park, Northampton- shire, July and August, 1849.'^ Among the Copepoda, as among the Cladocera, there are several species of so general a distribution that their occurrence may be predicted as much in one county as in another, and the notification of it in any particular locality is almost a matter of chance. It is therefore an odd coincidence that Dr. G. S. Brady in his British Copepoda should not expressly record for this county any of the common and well-known species, but on the other hand should record for it one that was, at any rate at the date of his book, a new and rare one. In 1880 he winds up the description of his Canthocamptus trispinosus, n. sp., with the words, ' Length one twenty-fifth of an inch (one mm.). Male unknown,' and observes, ' the only known locality for this species is the river Nene at Peterborough, where I took it sparingly in a little woody inlet." It belongs to the family Harpacticidce and to the genus Canthocampus instituted by J. O. Westwood in 1836. The name is evidently com- pounded of two Greek words meaning a thorn and a bend, since West- wood himself explains that the species ' have the abdomen of the females recurved with a spine beneath at the base.' * On pretence of correction authors have since almost invariably falsified the spelling into Cantho- camptus, changing the second half which is not really wrong and leaving unaltered the first half, which is evidently derived from acantha, a spine, ' Zeitichiift far tvissenschaftliche Zoolope, vol. xxv. p. 277 (1875). ^ Baird, British Entomostraca, Ray Soc, p. 109, 1850; Dr. Jules Richard, Annaks da Sciences Nalurelles, Zoologie, ser. 7, vol. xviii. p. 336 (1895). 3 Brady, A Monograph of British Copepoda, Ray Soc, vol. ii. p. 55, pi. 45, figs, i 5-22- 'Cyclops' (1836). 105
 * J. O. Westwood, The Entomologist's Text Book p. l 1 5 (1838); Partington's Cycloptedia, Art.