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 A HISTORY OF NORTHAMPTONSHIRE teen segments is partly free and slightly mobile. At the base of the outer antenna in the crayfish there is a large flat hair-fringed scale, in place of which the lobster has only a small spike. Less obvious, but not less important, are the differences in the branchiae or gills. Those known as podobranchis have the stem longitudinally split in the lobster but not in the crayfish, and of the so-called pleuro-branchix some are rudimentary in the crayfish which in the lobster are well developed. Further details might be added, but these are enough to show that in natural history a hasty glance will not always safely determine genera and species. Around the technical name of the crayfish a certain amount of controversy still hovers. Huxley himself begins his book by calling our English species Astacus Jiuviatilis, but ends by calling it, though with some reserve, Astacus torrentium} Dr. Walter Faxon, an American expert, decides that our species should be named Astacus pallipes? But, what- ever may be right for the second name, I personally am convinced that the first or generic name is properly Potamobius, and practically Huxley supports this view by placing it in the family Potamobiidce, the name of which can only be sustained by upholding the genus Potamobius for the English crayfish.^ The gastronomic value of the species has long been recognized. Its educational value is now even more highly appreciated. Both this and its claim to belong to the fauna of this county are attested by the following quotation. Mr. Beeby Thompson, F.C.S., F.L.S., of North- ampton, writing in December, 1886, says : — ' Several crayfish were recently required for dissection at the Science School, and one of the students undertook to procure them. The speci- mens were obtained from a shallow part of the river [Nene] near St. Andrew's Mill. I know that Cray-fish or Caw-fish [.? misprint for Craw- fish], as they are commonly called, have been found at this spot for thirty years, but I never saw them or heard of them being found at any other place near Northampton. Perhaps some of our members can give informa- tion as to other localities that they inhabit. I for one should be glad to know of such. I may say that two of the specimens caught last May have been in my aquarium ever since, and seem now to be in good condition. They are most interesting animals to watch ; the way in which they seize and devour minute joints of meat shows that they are not altogether free from the occasional human feeling of selfishness. Each of the cray- fish has shed its skin once since it became an inhabitant of the present restricted abode. To see one of these crustaceans shed its covering is one of the things I am still desiring ; it seems marvellous how they can get out of it so as to leave such a perfect case of themselves. They appear to hide themselves under the stones much more about the time of shedding their covering, and particularly after it, than at other times. ed. p. 296 (1881). ' Proceedings of the /American Academy of Arts and Sciences, vol. xx. p. i 54 (1884). ' Annals and Magazine of Natural History, ser. 6, vol. xix. p. 1 20. 102
 * The Cra^^sh, an Introduction to the study of Zoology, International Scientific Series, vol. xxviii. 3rd