466 ONISCID.E. 



I SOP DA . ONISCIDM. 



NOR if ALIA. 



Genus— ONISCUS. (Unnceus.) 



Generic character. Ovate, sub-depressed. Cephalon with 

 large lateral lobes extending outwards beneath the eyes. Outer 

 antennae eight-jointed ; second joint dilated at the base ; seventh 

 and eighth joints sub-confluent. Coxse of the first, second, and 

 sixth segments of pleon obsolete; third to the fifth, broad and 

 curved, acute at tips. Terminal uropoda posteriorly exserted ; 

 apical portion ovate, pointed at tip. Inner lobe linear, short, 

 extending slightly beyond the telson, which is convex. 



The species of this genus are typical of the family, 

 commonly called wood-lice, and are distinguished from 

 the other equally common species by having the ter- 

 minal portion of the outer antennse composed of three 

 joints, of which, however, the articulation between the 

 last and preceding joint is less distinct than the pre- 

 ceding. 



The Philoscm, which have also eight-jointed setose 

 antennae, are distinguished at once from the Onisci by 

 the narrowness of the segments of the tail and the length 

 of its exserted terminal appendages. 



*' The external angles of the superior margin of the 

 third ring of the head are produced into a broad lobe, 

 which covers over the origin of the external antennae ; 

 it is then continued across, projecting slightly over the 

 frontal line of the cephalic segment ; the transverse 

 suture is well marked ; the second ring very narrow, 

 almost obsolete. The lateral lobes are continued back- 

 wards, and are separated by a suture from the external 



