BRITISH ASSOCIATION. 271 



The internal (accessory filament), on the other hand, is rounded, 

 spine-like, generally made up of more than one articulation, and termi- 

 nates in a hollow hair, or rather becomes filamentous, presenting, in 

 short, all the characters of a true accessory appendage ; it is from this 

 character I have named it the accessory filament. 



Having established these relations, next for a detailed description of 

 the entire organs, i. e. first, the peduncle or basis ; second, ischium ; 

 third, accessory filament. 



1. The Peduncle or Basis. — This is attached to last abdominal ring, 

 and is either somewhat quadrilateral, without distinct lateral process, 

 its inner margin dilated into a lobe (Ligia). 



Or else somewhat triangular ; its internal margin produced into a 

 rounded process, which bears the accessory filament (Philoscia, Oniscus). 



The lateral process (obsolete in Tylos) is either distinct, produced 

 beyond, and arising from inner angle of the apex of the peduncle (Ligi- 

 dium), arising from near the base of the peduncle (Oniscus, Porcellio); 

 or else indistinct, and almost on the same level as the apex (Ligia); be- 

 tween these, every gradation of development exists. The peduncle may, 

 in fine, be described in general terms as a flattened articulation, gene- 

 rally furnished internally with an accessory appendage, bearing the 

 ischium on its summit, and more or less covered by the last abdominal 

 ring, from whence it arises. 



2. The Ischium or External Appendage. — This articulates 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 (?), SphaBrillo). 



Eounded, 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 suflicient 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). 



