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woodlice, is as truly a terrestrial species, and found at as great a dis- 

 tance from sea, as Porcellio itself. Most of his descriptions of genera 

 are avowedly mere transcripts from previous authors, even those which 

 one would suppose ought to have come under his own notice, being in- 

 digenous, as in the case of Philoscia, which he allies to Oniscus, whereas 

 in truth it is much more closely allied to Ligia in all its characters. His 

 specific descriptions are almost aU mere details of colour, without one 

 truly distinctive character. 



Dana has much extended the group, uniting, however, to the genera 

 already mentioned others, whose claim to the alliance appears but slight, 

 viz., the Limnoriffi and AscUidee, on account of the characters of the 

 posterior pair of abdominal appendages. He has thus made one large 

 group, Oniscoidea, and in his definitions has largely entered into cha- 

 racters which may be generic. 



He divides the Oniscoidea into three groups, according to the mode 

 of articulation of the body ; the number of articulations of the abdomen ; 

 the size of the last abdominal segment ; the length of the caudal appen- 

 dages (i. e. the last false feet) ; the absence or presence of a palp to the 

 mandibles; and the number of articulations and size of the internal 

 antennae. (Of these, the characters of the number of articulations in 

 the abdomen and internal antennae, the size of last abdominal segment, 

 presence of a palp to the mandibles, have reference solely to his last family 

 (Asellidae), a group which had been probably better omitted.) 1. Ar- 

 madillidae, according to arrangement of caudal appendages, divided into 

 Tylinae (Tylus), and Armadillinae (Armadillo, Sphaerillo, Armadillidium, 

 Diploexochus). 2. Oniscidae, according to number and form of articu- 

 lations of maxilliped, form of articulation of fifth joint of external an- 

 tennae, and form of peduncle and styles of caudal appendages, divided 

 into Oniscinae, Oniscus (including as sub-genera Trichoniscus, Porcellio, 

 Oniscus). Philoscia; Platyarthus; Deto. Scyphacinae (Scyphax, Stylo- 

 niscus). Liginae (Ligia, Ligidium). 3. Asellidae, including Limnorinae 

 (Limnoria). Asellinae (Jaera, Jaeridina, Asellus, Janira, Henopomus, 

 Munna). As I believe these last do not really belong to this group, I 

 omit their characters. 



Although this classification contains some new characters, many 

 genera are omitted, which naturally belong to the group, and many of 

 the characters are too artificial to be taken into account. The innova- 

 tion of considering Porcellio, Oniscus, and Trichoniscus as sub-genera 

 is highly objectionable (indeed it will be well when the term sub-genus 

 is banished altogether from our nomenclature), as these divisions do not 

 depend, as he seems to assert, on the mere number of joints in the ter- 

 minal filament of the antennae, but, as I hope to prove, on a number of 

 other characters sufl&cient to constitute them, as real genera as Ligia 

 and Ligidum. Mere number plays too great a part in his system also to 

 allow of natural groupings. His classification, however, is valuable as 

 restoring to their proper place the Armadillidae, which, on account of 

 their resemblance to certain Myriapodae, have been hitherto, as it seems, 

 unjustly degraded to the bottom of the list of Cloportides. 



