270 PROCEEDINGS OF SOCIETIES. 



the interior border being produced into a lobe, and attached to the ex- 

 treme exterior edge of the last ring, or rather to a process of this ring, 

 visible only below, and which may be looked on as the coxa reduced to 

 a minimum and fixed to the ring ; the form of articulation is the same 

 as in Ligia. 



This view of relations receives further confirmation on examination 

 of the last abdominal ring in Philoscia and kindred forms, where the 

 articulation is completed externally by a small triangular lobe, differing 

 from the angle in Ligia only in size ; indeed, it is a question whether 

 I am strictly correct in describing Philoscia as wanting the "coxa" 

 in the sixth abdominal ring, and not as having the coxae fused to the 

 ring. 



The mode of articulation dependent on the development of coxae in 

 the last ring causes the peduncle to be more or less uncovered by the 

 preceding coxae, and has given rise to the erroneous description of 

 Brandt, already referred to, viz., "Ligiae — Caudal appendages, one pair" 

 (Conspect., page 9); Oniscinae — " Caudal appendages, two pairs" (ib., page 

 12); the absence, or rather complete fusion, of the coxa with the last 

 ring causing the peduncle inOniscus, &c, to be completely covered by the 

 coxae of the fifth rings, led Brandt to overlook its existence altogether, 

 and to mistake the terminal appendages for separate organs. 



2nd. The mode of articulation of the so-called external appendage 

 (ischium), and the peduncle (basis). 



This is always at the extremity of the peduncle, and generally on a 

 plane inferior to that of the so-called internal appendage, the peduncle 

 being hollowed out into a regular joint for its reception, and the exter- 

 nal border of the peduncle terminating inferiorly in a tooth outside the 

 articulation ; the internal, on the other hand, arising from a lateral pro- 

 cess, more or less distinctly marked, and generally on a plane, much 

 superior to the articulation of the external appendage. This is evident, 

 even in such forms as Ligia, where the apex of the peduncle being trun- 

 cated, the appendages arise from nearly the same point, the lateral pro- 

 cess being slightly larger than the real apex, or as Ligidium, in which the 

 lateral process is still further elongated, so that the ischium appears 

 to arise above the internal appendage. 



From this extreme we trace the lateral process till we arrive at such 

 forms as Oniscus, where, without careful examination, we might doubt 

 its existence at all, and where, to a superficial examination, the internal 

 appendage appears to have no connexion with the peduncle at all, but 

 rather to spring directly from the last ring : but more of this genus anon. 



3. The difference in form and relations between the external 

 (ischium) and internal (accessory filament) appendages. 



Besides the difference between these two, displayed in the fact of the 

 one (ischium) being articulated to the extremity, the other (accessory 

 filament) to the lateral process of the peduncle, the differences of the two 

 are remarkable. 



The external (ischium) is generally more or less compressed, often 

 abrupt at its termination, and generally ending in a tuft of hairs. 



