736 DR WALTER E. COLLINGE. 



with outer lobe terminating in a series of stout, curved spines, inner lobe terminating 

 in two to four setose spines. Second maxillae each consist of three lobes fringed with 

 setae. Maxillipedes operculiform, palp with three to five joints. Mesosomatic seg- 

 ments, excepting the first, usually about equal in length, coxal plates distinct or 

 coalesced with the segments. Thoracic appendages uniform in structure, ambulatory, 

 varying in size from before backwards, usually stronger in male than in female, occa- 

 sionally approaching a subcheliform character ; dactylus strong, unguiform, unequally 

 bi-dentate. Metasome with some or all of the segments fused to form a large terminal 

 scute-like segment. Metasomatic appendages laminate. Uropoda inferior, arching 

 over the ventral side of the metasome and enclosing the appendages. 



Key to the Genera of British Iboteibm. 



1. Body ovate, oblong, or elongate, more or less depressed. 

 Antennae with multiarticulate flagellum. 

 Maxillipedes with four-jointed palp. 



Coxal plates of the mesosomatic segments, excepting the first, distinctly 



separated. 

 Metasome composed of three segments. 



Idotea, Fabricius. 



2. Body somewhat slender, long and narrow, with parallel sides. 



Antennae short, with single-jointed flagellum, or with restricted number of 



joints. 

 Maxillipedes with five-jointed palp. 



Coxal plates of the mesosomatic segments distinct, but small and narrow. 

 Metasome composed of three to five segments. 



Zenobiana, Stebbing. 



3. Body oblong, moderately convex, usually with indications of a keel. 

 Antennae with multiarticulate flagellum. 



Maxillipedes with four-jointed palp. 

 Coxal plates small, but distinct. 

 Metasome composed of a single segment. 



Synisoma, Collinge. 



1. Genus Idotea, Fabricius. 

 Idotea, Fabricius, J. C, Suppl. Entom. Syst., 1798, p. 302. 



Body ovate, oblong or elongate, more or less depressed. Cephalon subquadrate, 

 not expanded laterally, sometimes with lateral clefts or posterior sinuous furrow. 

 Coxal plates of mesosome usually well defined on the second to seventh segments. 

 Eyes dorso-lateral. Antennulae with short, clavate flagellum. Antennae with 



