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Show 752 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 4, O n the Classification and the Distribution of the Crayfishes. B y T. H . H U X L E Y , Sec. R.S., V.P.Z.S. [Eeceived May 23, 1878.] I. Introduction, p. 752. II. The Modifications of the Branchiae in the Crayfishes, p. 756. 1. The branchiae of Astacus, p. 756. 2. The branchiae of Cambarus, p 763. 3. The branchiae of Astacopsis, p. 764. 4. The branchiae of Chceraps, p. 768. 5. The branchiae of Engceus, p. 769. 6. The branchiae of Paranephrops, p. 770. 7. The branchiae of Parastacus, p. 771. 8. The branchiae of Astacoides, p. 773. III. The Classification of the Crayfishes, p. 775. IV. The Distribution of the Crayfishes considered in relation to their morphological differences, p. 786. I. INTRODUCTION. The dismemberment of the genus Astacus oi the older naturalists, down to the time of Fabricius, was commenced by Leach, who separated the Norway Lobster as the type of a new genus, Nephrops *. Milne-Edwards advanced a step further by establishing the genus Homarus for the Lobsters, and leaving only the freshwater Astaci, or the proper Crayfishes, in Astacus*. The later proposal of Leach, to use Astacus for the Lobsters, and to give a new generic name (Potamobius) to the freshwater Crayfishes, would have had the advantage of retaining the primitive signification of aaraKos. But Potamobius had already been used in another sense; and the change introduced by Milne-Edwards is so generally adopted that it would be confusing to attempt any further alteration. Guerin 3 next proposed to distinguish the Astacus madagascariensis of Audouin and Milne-Edwards, as Astacoides, from the other Crayfishes ; and Erichson, in his valuable Monograph of the group4, adopts Astacoides for the Madagascar and some of the Australian forms, and establishes the new genera Cambarus, Chceraps, and Engeeus. In Cambarus and Chceraps the number of the branchiae is taken into account as an important generic character. In 18425 Mr. Adam "White described some Crayfish from New Zealand, for which he constituted a new genus, Paranephrops, under the impression that the New-Zealand form approximated to the genus Nephrops. Mr. Wood-Mason6 has since "denied the existence of any special relationship between the New-Zealand 1 Leach, Trans. Linn. Soc. xi. 344. 2 'Histoire Naturelle des Crustaces,' 1837. 3 Bevue Zoologique, 1839. 4 " Uebersicht d. Gattung Astacus," Archiv fiir Naturgeschiehte, Bd. 6. 5 Gray's'Zoological Miscellany.' See also Dieffenbach's ' New Zealand,' 1843, vol. ii. p. 267. 6 Proc. Asiat. Soc. Bengal, 1876, p. 4. |
