TERRESTRIAL ISOPODS. 83 



of the segments of the mesosome being armed with small spines, 

 and, in the male, by the conspicuous copulative organs. These 

 latter I have dissected out, and they agree with the details 

 given by Sars — " Inner ramus of first pair of pleopoda greatly 

 produced, with the terminal joint narrow knife-shaped; that of 

 the second pair bi-articulate, proximal joint very short, distal 

 joint long and slender, styliform." I have met this species in 

 company with T. roseus in two localities (3, 4). While moving 

 about it cannot very readily be distinguished from the young 

 forms of that species of approximately the same size (about 

 2 mm.), as the difference in colour is not discernible, although, 

 by watching closely, the movements of one of the species 

 (T. roseus) are seen to be appreciably quicker. Under the 

 microscope, however, the following differences are revealed : — 

 In T. roseus the colour, as a rale, in these young specimens 

 is uniformly light orange, while in T. pygmaeus it is whitish, 

 with a few light-red pigmentary ramifications across the seg- 

 ments of the mesosome. The eyes in T. roseus appear to consist 

 of a single visual element, while in T. pygmaeus there are three 

 visual elements, which are arranged in a triangular form. The 

 tubercles of the dorsal face are more prominent in T. iwseus, and 

 the flagellum of the antennse is usually quite distinctly four- 

 articulate, even at this early stage of growth. Length of adult 

 male, 2 mm. ; of female, about 2 h mm. 



Occurrence. — (1) Field near Carntyne Road, Glasgow; (2) 

 field, Cumbernauld Road, Glasgow; (3) conservatory, People's 

 Palace, Glasgow; (4) Camphill Gardens, Glasgow; (5) field, 

 Poplar Park, Lanark ; (6) road near Wemyss Bay Station. 



This species is apparently new to Great Britain. It has been 

 recorded by Sars for the vicinity of Christiania, Norway. 



Genus Porcellio, Latr., 1804. 



Porcellio dilatatus, Brandt, is closely allied to the common 

 form, P. scaber, Latr., but may be readily distinguished from 

 that species by its unusually broad body and by the shape of 

 the last segment of the metasome, which is rounded at the tip 

 and is not dorsally grooved. It is not so strongly tuberculated 

 as is P. scaber. The colour is dark slaty-grey, but somewhat 



