A REVISION OF THE BRITISH IDOTEID^}. 733 



Colidotea, Richardson, Edotia, Guerin-Men., Crabyzos, S. Bate, Eusymmerus, 

 Richardson, Erichsonella, Benedict, Pentias, Richardson, Paridotea, Stebbing, and 

 Synisoma, Collinge, the fusion is complete, the segments being represented by 

 a single piece. In nearly all cases there are evidences of one or more suture lines 

 indicating a further segment or segments. 



1. Appendages. — There are five pairs of appendages, each of which consists of 

 a basal segment carrying two elongate-oval lamellae fringed with long setae. The 

 inner lamellae of the second pair, and of the first pair also, in Pseudidothea, Ohlin, 

 in the male bears a fine stylet. 



2. Uropoda. — This pair of appendages differs in this family, in common with 

 other members of the suborder Valvifera, from the condition obtaining in any 

 other Isopoda. Here they consist of a pair of somewhat flattened, opercular-like 

 plates (the protopodites) closing within the metasomatic appendages, by meeting in 

 the mid-ventral line or overlapping one another. Each is attached to the metasome 

 laterally. Posteriorly there is in most genera a hinge dividing off a posterior plate 

 (the endopodite). In some genera, e.g. Mesidotea, Richardson, Chiridotea, Harger, 

 Glyptonotus, Eights, and Macrochiridothea, Ohlin, there is an inner plate to each 

 uropod (the exopodite). Articulating laterally on the outer side, or dorso-laterally, 

 there is usually a plumose style. Stebbing (70) states that this is absent in 

 Paridotea ; and in Symmius, Richardson, the endopodite is not present, each 

 uropod consisting of a single piece. 



VII. Bionomics and Economics. 



Very little is known as to the life-history and habits of the family of Isopods 

 here treated of. Roux (63) has given some interesting details of their habits, and 

 Issel (34) has studied the tube-dwelling species of the genus Zenobiana. 



Whilst the family contains some of the largest known Isopods, some are 

 quite small. 



Many species are exceedingly plentiful. Most of them seem to prefer decaying 

 masses of algae in rock pools or still water, where they feed upon dead fishes, 

 molluscs, crustaceans, annelids, etc. 



Although the majority of species are marine, Loven has recorded Mesidotea 

 entomon from deep Scandinavian lakes, and Thomson (77) has described a species of 

 Idotea (lacustris) from a fresh-water lagoon in New Zealand. 



Roux remarks that when the sea is rough they seek deep water, and are often 

 thrown back by the action of the waves. This is so in St Andrews Bay, where, 

 after a rough sea, large numbers of the commoner species are to be found clinging 

 to the algae in the rock pools. 



Idotea baltica progresses by a series of short, jerky jumps, whereas /. linearis 

 moves less rapidly, often apparently floating with the uropoda open and hanging 



