( 16 ) 



2. The Ischium or External Appendage. — This articiilatcs to the apex 

 of the basis or peduncle, and is either — 



Rounded, its base dilated and flattened, hairy and scabrous; its 

 apex abrupt and tufted with hairs (Ligia, Philoscia, Scyphax, Ligi- 

 dium(?), Tylos(?), Sphajrillo). 



Rounded, somewhat subulate, its base slightly dilated and com- 

 pressed, smooth (Philougria, Itea (?), Titanethes (?), Styloniscus (?). 



Flattened, acuminate, dilated, hairy, scabrous (Oniscus, Porcellio, 

 Scyphax (?)). 



Flattened, dilated, squared, apex truncate or rounded, broader 

 below than above, hairy (Armadillium, Actecia (?), Armadillo). 



Accessory filament or internal appendage, either — 



Tapering, rounded, terminating in a jointed filamentous hair (Li- 

 gia, Philoscia, Philougria), or — 



Flattened, apex truncate, wider than base, club-shaped, fringed 

 with hairs (Armadillium) ; or — 



Obsolete (Tylos). 



The published details of foreign genera are so inaccurate that I must 

 confine myself mainly to our native species in my description of types, 

 merely glancing at one or two of the former, of which sufficient details 

 have been published. Those which have no British representatives are 

 marked with an asterisk. 



1. ^Peduncle operculiform, triangular, broader above than below, ar- 

 ticulated beneath last abdominal ring. Lateral process obsolete ; ischium 

 short, subulate (?), articulated to apex of peduncle. Accessory appen- 

 dage, none (Tylos). 



2. Peduncle irregularly quadrilateral, much broader than long, outer 

 side produced, articulated by lower margin beneath exterior angle of 

 posterior border of the last ring ; entire peduncle almost covered by the 

 ring. Accessory lobe triangular, springing from base of peduncle, 

 scarcely half length of peduncle. Ischium irregularly quadrilateral, 

 base much narrower than apex, which is transverse; inner side pro- 

 duced at apex, borders hairy. Accessory appendage nearly twice length 

 of ischium ; base rounded, narrow ; apex flattened, club-shaped, hairy 

 and scabrous (Armadillium, Armadillo (?). To this neighbours, probably, 

 Sphaerillo and Diploexochus). Plate XXI., Figs. 12, 13. 



3. Peduncle triangular, much longer than broad, articulating border 

 notched at outer angle, outer margin produced into lobe at base, apical 

 angle well marked, apex half breadth of base, articulated to exterior 

 angle of last ring beneath. Accessory lobe distinct, quadiilateral, about 

 third length of peduncle, arising from articulating margin, completely 

 covered by last abdominal ring. Ischium compressed, acuminate, tri- 

 gonal, lobed on inner side, hairy. Accessory appendage curved, tri- 

 gonal at apex, lobed at base, terminating in filament, two-thirds con- 

 cealed beneath terminal ring, two-thirds length of ischium (Porcellio, 

 Oniscus (which has accessory lobe nearly obsolete), Platyarthus, pro- 

 bably). Plate XX., Fig. 11. 



. 4. P«rfww^/<9 quadrilateral, transverse, twice as broad as long, superior 

 rticulating border produced into an angle, articulated to lateral border 



