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Show 302 DR. H. J. HANSEN ON THE [Nov. 29. 4. On the Morphology and Classification of the Asellota- Gronp of Crustaceans, with Descriptions of the Genus Stenetrium Hasw. and its Species. By H. J. H a n s e n , Ph.D., F.M.L.S. [Received October 17, 1904.] (Plates X IX .-X X I * .) I. Introductory Remarks. The tribe or suborder Asellota is in some respects one of the most varied and, as to the number of species, probably by far the richest of all groups of pre-eminently marine Isopoda. A perusal of the portion in question of Beddard's account of the ‘ Challenger ' Isopoda (Zoology, vol. xvii.), and of G. O. Sars's ‘ An Account of the Crustacea of Norway,' vol. ii. Isopoda, 1896-99, conveys a fair idea as to the striking differences in general aspect and in some structural features between the numerous genera, among which we find such types as Asellus Geoff., Ianira Leach, Munna ELr., Dendrotion G. 0. S., Macrostylis G. 0. S., Ischnosoma G. O. S., Desmosoma G. 0. S., Munnopsis M. Sars, Eurycope G. O. S. In the work named, Sars describes 42 species referred to 21 genera; Beddard has established 32 species referred to 15 genera, and 8 of these genera are not found in Norway. In order to furnish an instance showing how much remains to be known, I may perhaps state here that from the seas around Greenland, Iceland, and the Faroe Islands, the Copenhagen Museum possesses more than 90 species, of which at least 60 are new to science ; the major part of these new forms were secured by the ‘ Ingolf ' in depths between 300 and 1870 fathoms. Sars refers his 21 genera to five families, but it will be shown below that four of these are almost artificial, as really good characters for their separation are wanting. But this distinguished author has produced a vast number of good figures-with useful descriptions-of all his forms and of details of their dermo-skeleton; moreover almost all really important genera hitherto established of Asellota have been incorporated in his fine work. For these reasons I can often, in the following discussion, refer the reader to his figures as proofs and illustrations for my remarks. Among the genera not represented in the Norwegian fauna, Stenetrium Haswell is the most aberrant and important. Of this genus five species have been established by four authors, but our knowledge of several essential points of its structure, especially of the pleopoda, is still imperfect. Most of the figures of S. antillense, sp. n., were drawn by me more than fifteen years ago, but publication was, however, postponed, which proved to be fortunate, as new and interesting species have been received in * For explanation of the Plates, see p. 330. |
