374 A HISTORY OF RECENT CRUSTACEA 
Idotea lacustris, Thomson, from New Zealand, can 
make itself at home in fresh water. It has been taken by 
Mr. Chilton in Mihiwaka Creek, a mountain stream, at 
200 feet or more above the sea-level. The young leave 
the marsupium with all the segments developed and their 
appendages present, but the second antennze having a 
single-jointed instead of a multiarticulate flagellum. 
Idotea prismatica (Risso) belongs to a section in which 
the pleon is composed of four or five instead of only three 
more or less distinct segments, and in which the species 
are small, with a few-jointed flagellum to the second 
antenne. It has a small outer branch to the uropods. 
It is found in North and South Devon, and has been de- 
scribed by Bate and Westwood as Idotea parallela. Itisa 
question whether a separate genus ought not to be named 
for the group of species to which it belongs. Zenobia, 
Risso, 1826, in which it was originally placed, is a preoc- 
cupied name. 
Idotea acuminata (Leach) belongs to a section in which 
all the segments of the pleon are dorsally fused and form a 
single piece. In Idotea appendiculata (Risso) it has a 
synonym, the two different forms of pleon being connected 
by numerous gradations. The species is found in North 
and South Devon, and in the Clyde as well as in the 
Mediterranean. For the group to which it belongs perhaps 
the genus Leptosoma, Risso, 1826, should be upheld, with 
a substitute for the name which again is preoccupied. 
Miers includes in this group the Australian Crabyzos longi- 
caudatus, Spence Bate, 1863, although in that species the 
head is fused with the first segment of the perzeon. 
Edotia, Guérin-Méneville, 1829-44, has the body 
rather couvex, and the pleon one- or two-jointed. The 
second antennz are either short with an obsolete or rudi- 
mentary flagellum, or well developed. The limbs of the 
perzon have the seventh joint strong, the sixth joint in 
the first three pairs not greatly dilated. The uropods have 
the basal plates crossed by an oblique line. The Arctic 
Edotia bieuspida (Owen) is beautifully coloured. It has 
the second antenne well developed. Ldotia triléba (Say) 
