728 DR WALTER E. COLLINGE. 



Edotia nodulosa, Krciyer, at a depth of 190 fathoms, oft' Halifax, U.S.A., and 

 Mesidotea entomon (Linn.) has been recorded from 60 fathoms. 



Some species, like I. baltica (Pallas), are cosmopolitan, whilst others have a very 

 restricted distribution. The whole question of the distribution of the different 

 genera would well repay further investigation. 



Zenobiana, Stebbing, and Synisoma, Cllge. ( = Stenosoma, Auctt.), would seem to 

 be rare in northern waters around the British Isles, although Bate and West- 

 wood (3) mention having received examples of S. acuminata (Leach) from Cumbrae. 

 The latter genus has probably a southern distribution. It is recorded from 

 numerous localities on the shores of the Mediterranean, Adriatic, and Black Seas, 

 and also from the southern coast of England. 



Of our British species of this family, the majority of the species of Idotea are 

 common round the coasts of the British Islands. /. metallica, Bosc, and /. viridis 

 (Slabber) are perhaps rarer than the remainder. /. sarsi has, so far, only been 

 received from St Andrews Bay. 



I have elsewhere (15) pointed out that of the eight previously recorded British 

 species of Idotea, seven have been found in St Andrews Bay, viz. : — 



i". baltica (Pallas) ; /. pelagica, Leach ; /. neglecta, G. 0. Sars ; /. emarginata, 

 Fabr. ; /. granulosa, Rathke ; /. viridis (Slabber) ; /. linearis (Pennant). 



V. Variation. 



Apart from the colour markings, which are endless, and slight variations in the 

 mandibles and first and second maxillae, very few variations have been met with in 

 the large number of specimens I have examined. In /. baltica (Pallas) Bate and 

 Westwood (3, p. 381) give figures of variations in the form of the terminal segment 

 of the body. Some of these are undoubtedly of young examples, or possibly were 

 not referable to this species. In the form of the antennae, apart from the number of 

 joints in the fiagellum, and in the shape of the terminal segment, I have found very 

 few variations indeed, and Sars (64, p. 81) states that he has found the form of the 

 terminal segment of the metasome pretty constant, even in young specimens. 

 According to Chilton (ll), the segmentation of the metasome is liable to vary in a 

 species. As an instance he cites the difference in Idotea peronii, M.-Edw., and 

 /. stricta, Dana, and unites the two species. 



Miers (44) was of opinion that there were several distinct geographical sub- 

 species or varieties of /. baltica, and I fully concur with this view. Thus in 

 St Andrews Bay the ordinary large form occurs in great abundance, exhibiting 

 innumerable colour variations ; but there is also a very much rarer and smaller form, 

 which is found only, so far as my observations go, on the algae in the rock pools on 

 the east shore. It is by no means common, for diligent search has so far only 

 resulted in obtaining eight specimens. 



