190 DUBLIN UNIVERSITY 



ment to Armadillium, the lobes, both lateral and frontal, being derived 

 from the cephalic or mandibular (i. e. fourth) somite, and not from 

 the third, or second antennary. This latter is but badly developed 

 here, and small ; but at the same time, the distinctions between it and 

 the fourth somite are distinctly appreciable on a careful examination. 



The articulation between the posterior pleopod and the telson (last 

 ring) is very remarkable. The telson is totally devoid of coxae, and 

 the ring continued beneath the body terminates abruptly on either side 

 in a rounded lobe, so that the central portion of the body underneath is 

 unprotected, the ring being wanting in the median line. The posterior 

 pleopods are articulated to the superior border of the inferior (sternal ?) 

 part of the ring, a little internal to the external lateral angle, by a well- 

 marked ball and socket joint, so that at first sight it appears as though 

 these appendages were derived from the penultimate (fifth) somite, and 

 not from the telson. * 



The internal antennae are three-jointed, i. e. a peduncle and a two- 

 jointed filament. I find this arrangement of parts in nearly all the 

 Oniscoids I have examined, and therefore conclude that it is the 

 normal arrangement of parts in this group, and characteristic of them. 



Family.— POItCELLIOlSTD^. 



Genus 3. — Platyartheus {Brandt). 

 (n\aTvs apOpos.) 



Telson (cingulum ultimum) coxis obsoletis. Pleopoda posteriora 

 (pedes spurii) sub nuda, ad telson angulum superiorem externo-latera- 

 lem, articulata, basis subrotundus; Ischium trigonum, satis appendi- 

 culatum. Antennae internee 3-articulatae. Antenn. extern, basis, 

 articulus 2dus minute-lobatus, articulus 5tus dilatatus compressus. 

 Filamentum 2-articulatum. Abdominis cingulum, coxae lmi et 2di 

 obsoletae, 3tii, 4ti, 5tique magnae. Carapax frontaliter et lateraliter 

 lobatus. Species, una, P. Hoffmannseggii. 



1. — Platyarthrus Hoffmannseggii (Br.). 



Corpore omnino dense scabro; cingulum marginibus tuberculis 

 scabris crenulatis. Fronte arcuato, lobato; lobis lateralibus, prominenti- 

 bus; lobo frontali arcuato setis crassis ornato. Antennis ut genus, 

 scabris et hirtis. Cephalothorax : cingulum coxis bene productis. 



