ORAL APPENDAGES IN SOME TERRESTRIAL ISOPODS. 289 



1. LiGIA OCEANICA, Linn. (PI. 20. tigs. 1-4.) 



Thirty-six specimens have been examined and four variations, one in 

 each of the oral appendages, have been observed. The one in the mandibles 

 occurred twice and on the right side of the body only in both cases, that in 

 the first maxillse once, and those in the second maxillse and maxiliipedes each 

 twice. The specimens examined were collected from two localities. 



llie Mandibles. — The variation shown in fig. 1 occurred twice. In the 

 curved form of the teeth, it is quite distinct from the figure given by Sars (5) 

 and approaches most closely that given by Hewitt (3). 



2'he 1st Maxillce. — The only variation noted was in a single specimen from 

 St. Andrews (fig. 2) in which the setose bristles of the inner lobe were larger 

 than usual and the short thick s{)ines of the outer lobe reduced to two, the 

 distal extremity of the lobe forming a knob-like process. 



The 2nd Maxillce. — In two examples the terminal portion of the protopodite 

 was thickened and the two setose bristles rather Lirger than usual, whilst 

 externally the thickening is produced into a tooth-like spine (fig. o). 



The Maxiliipedes. — In two examples the inner plate was found to have the 

 spines unusually well developed in addition to the greater length of those at 

 the extreme distal end there were present four spines just below these 

 (fig. 4, sp.). The outer palp was considerably longer than usual, and further 

 differed from the normal in the number and length of the spines (tig. 4). 



2. Trichoniscus roseus [Koch) Bndde-Lund. (PI. 20. fig. 5.) 

 Forty-eight specimens were examined of this interesting species^ but only 



one variation was observed, which occurred in the maxiliipedes of nine out 

 of nineteen specimens collected at Hale, Cheshire. In these (fig. 5) the 

 maxiliipedes were of a much more robust type than ordinary, and characterised 

 by three well-defined spines on the outer distal palp^ whilst the inner one 

 terminated in a spinous manner as in ty{)ical examples of T. pusillus, Brandt. 



3. Oniscus asellus, Linn. (PL 20. figs. 6-16 ; PI. 21. figs. 17, 18.) 



The oral appendages of one hundred and twelve specimens of this species 

 were examined and thirteen variations were observed. Of these six occurred 

 in the mandibles, three in the first maxillse, one in the second maxillse, and 

 three in the maxiliipedes. The variations in the form of the mandibles would 

 seem to be endless. The specimens examined were collected from three 

 localities. 



The Mandibles. — These are shown in figures 6-11. The first form (fig. 6) 

 occurred in three different specimenSj once on the right side and twice on the 

 left. In the general shape this variation differs from the typical form, being- 

 produced laterally in a triangular manner. There are three stout mandibular 

 teeth and three smaller pointed teeth partially overlapping these. The second 



