Classificatioit of the Crustacea Malacostraca. 145 



paper is to discuss somewhat more fully than is possible 

 within the limits of a text-book certain of the facts bearing 

 upon the case, to put into systematic form (with some modifi- 

 cations and additions) the classification suggested by 

 Dr. Hansen, and to invite criticism of the result. 



In 1815 Leach *, adopting a basis of classification which 

 had previously been applied by Lamarck to the whole class 

 of Crustacea, divided the subclass Malacostraca into two 

 legions — thePodophthalmaandtheEdriophthalma — according 

 to the condition of the eyes, movably pedunculate in the ono 

 and sessile in the other. Without attempting to summarize 

 the numerous modifications which have been suggested, it 

 may be said that Leach's classification has been accepted in 

 principle by the majority of carcinologists since his time, and 

 is that most generally followed at the present day. As 

 originally defined, the two groups were sharply distinguished 

 from each other not only by the characters given by Leach, 

 but also by the presence in the Podophthalma of a cephalo- 

 thoracic shield or carapace which was absent in the Edrio- 

 phthalma, this character giving occasion for the names 

 Thoracostraca and Arthrostraca applied to them by Bur- 

 meisterf. The progress of research, however, rendered it 

 increasingly difficult to form satisfactory definitions of the 

 two divisions. In particular the recognition by Fritz Miiller 

 of a true, though reduced, carapace in the Tanaidaa and the 

 elucidation of the structure of the Cumacea begun by 

 H. Goodsir and by Kroyer provided intermediate links, the 

 Cumacea, indeed, being placed sometimes in the one group 

 and sometimes in the other. Claus \ established a third 

 division (Leptostraca) for Ntbalia and its allies, and the 

 separation of the Stomatopoda from the other Podophthalma, 

 first suggested, I believe, by Huxley §, left in the last-named 

 group only the Schizopoda and Decapoda. 



An important departure from the line of classification 

 generally followed was made in 1883 by Prof. Boas H, who 

 abandoned the group Schizopoda, pointing out that the Mysidse 

 and Lophogastridse were by no means closely related to the 



* " A Tabular View of the External Characters of Four Classes of 



Animals which Linne arranged under Insecta ," Trans. Linn. Soc. 



London, xi. (1815) pp. 306-400. 



t ' Beitrsige zur Naturgeschichte d^r Rankenfiisser,' Berlin, 1834, p. 55. 



% ' Grundziige der Zoologie,' 4te Aufl. (1880) p. 573. 



§ Introd. Classification Anini. (1869) p. 125; Manual Anat. Invert. 

 Animals (1877), p. 317. 



|| " Studien iiber die Verwaudtschaftsbeziehungen der Malakostraken," 

 Morpbol. Jahrb. viii. pp. 485-579, pis. xxi.-xxiv. (1883). 



Ann. & Mag. N. Hist. Ser. 7. Vol. xiii. 10 



