734 DR WALTER E. COLLINGE. 



perpendicular to the body. Most of the species are nocturnal, hiding under algae 

 during the day. Idotea linearis is fairly active during the daytime, gliding grace- 

 fully through the water even when strong sunlight was shining on the vessel in 

 which it was contained. In the rock pools also I have noticed this species active 

 during the daytime. 



Roux records that in the Mediterranean the fishermen collect these Isopods and 

 use them as bait. The method of collecting is by tying together bundles of fucus, 

 which are sunk below the water; on these the Idoteae assemble, and from time to 

 time the masses of algae are drawn up and the specimens collected. 



Fishes would seem to be the chief enemies of these Crustacea. Mr W. Ramsay 

 Smith, in his papers on the food of fishes,* has given many records of their 

 occurrence in the stomachs of various species, as has also Dr Thomas Scott in his 

 " Observations on the Food of Fishes." t I have records of the occurrence of all 

 the British species of Idotea, excepting viridis and metallica, from the stomachs of 

 the cod, haddock, and plaice. 



Matzdorff (43) has given a most interesting account of the colour variation in 

 /. haltica. The remarkable variability of this species has been frequently com- 

 mented upon. He enumerates and figures a number of colour varieties, and shows 

 that they are common to both sexes. The same individual changes colour by the 

 expansion or contraction of dark brown chromatophorous cells, adapting itself to its 

 surroundings. Thus specimens found near the surface, on the top of algae, were 

 light-coloured, while those on the bottom, in the same locality, were dark-coloured. 

 After the extirpation of the eyes the animals cease to undergo these colour changes. 



VIII. Systematic. 



Many genera of doubtful value have been made by different authors, often upon 

 very trivial differences. 



Dana (16), 1852, divided the family into the following five genera: — Idotea, 

 Fabr. ; Edotia, Guerin-Men. ; Erichsonia, Dana ; Cleantis, Dana ; and Epelys, Dana. 

 Bate and West wood (3), 1867, included all the British species in the genus Idotea, 

 Fabr. Miers (44), 1881, gives the following divisions : — 



Fam. IDOTEID^, Dana. 



Sub-fam. i. Glyptonotin.^. 



Genus (rlyptonotus, Eights. 



Sub-fam. ii. Idotein^e. 



Genera Idotea, Fabr. ; Edotia, Guerin-Men. ; and' Cleantis, Dana. 



BARGER (30) included the five genera: — Chiridotea, Harger ; Idotea, Fabr.; 

 Xi/nidotea, Harger ; Erichsonia, Dana ; and Epelys, Dana. Stebbing (68) recognised 



* 7th, 8tli, 9th, and 10th Reports of the Fishery Board of Scotland. 

 t Tbid., 20th Report, 1902, pp. 486-538. 



