260 PEOCEEDINGS OF SOCIETIES. 



has but recently come into my hands, and for the perusal of which I 

 have to thank the kindness of A. H. Haliday, Esq., entitled, "Prodro- 

 mus Synopseos Crustaceorum Prussicorum," published at Konigsburg, 

 1834, from the pen of E. G. Zaddach, Ph. D., which contains much 

 useful matter; among other things, M. Edward's error concerning Phi- 

 loscia is noticed. 



Dana in his splendid work on the Crustacea, has proposed in some 

 respects a new arrangement of the group, but has, as I think, mistaken 

 in some cases the bearings of the characters, as will be shown further 

 on. 



Valuable notices of separate genera and species have appeared as 

 detached papers in some of the journals, chiefly German (as, for instance, 

 the description of the curious genus, Titanethes albus of Schiodte (Phce- 

 rusa alba, Koch), in Schiodte' s interesting account of the subterranean 

 Eauna of Carniola), which have thrown much light on the true affinities 

 of these animals, and render a revision of our classification necessary. 



It will be necessary to glance at the systems of classifications adopted 

 by the several authors mentioned ; but first I must notice a most elabo- 

 rate, as far as illustrations go at least, work by Henrich Schaeffer, intended 

 as a supplement to Koch's " Eauna Germanica." In this work we have 

 spurious species multiplied to a most inconvenient extent, and his ge- 

 nera are most of them too large : thus, under Ligia he includes Philoscia 

 muscorum (figured as Ligia melanocephala, a more natural alliance, by the 

 way, than M. Edwards, of Oniscus). Itea includes Itea proper and 

 Platyarthus {Br.), and probably a third form. He has changed Brandt's 

 name, Ligidium, for Zia, and his Armadillo into Pentheus, whilst Arma- 

 dillium {Br.) figures here as Armadillo, Latr. The other genera described 

 by him are Phserusa, Oniscus, and Porcellio, the two latter including 

 as species many which can scarcely be looked on as even varieties. 



On Classification. 



Brandt, taking as familiar characters the number of joints in the termi- 

 nal appendages of the antennae and the number of pairs of caudal append- 

 ages (i. e. the last pair of false feet), has divided the genera known to 

 him into two sections, viz., Ligiea (Ligia and Ligidium) and Oniscinea, 

 subdivided according to the length, form, and insertion of the exterior 

 caudal appendages, into (1) Porcellionea (Trichoniscus, Platyarthus, 

 Porcellio, Philoscia) ; and (2) Armadillinea (Armadillidium, Cubaris, 

 Armadillo, and Diploexochus). 



Although these generic groups are natural enough, he appears to 

 have mistaken the true nature of the caudal appendages, which in all 

 the genera belonging to this group consists truly of two pairs, as we 

 hope to show when we come to treat more in detail of them, although 

 in all the groups except Ligiea their true nature is somewhat obscured 

 by the truncation of the margin of the peduncle. In Ligidium, included 

 by him among the Ligiea, but which, as will be seen, we propose to 

 place in a separate division, the appendages are really two pairs. 



His lesser divisions and species are many of them faulty, being 



