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 yonng leave 

 the marsupium with all the segments developed and their 

 appendages present, but the second antennae 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 

 antennse. 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. It is a 

 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 lonr/i- 

 caudatus, Spence Bate, 1863, although in that species the 

 head is fused with the first segment of the peraeon. 



Edotia, Guerin-Meneville, 1829-44, has the body 

 rather convex, and the pleon one- or two-jointed. The 

 second antennas are either short with an obsolete or rudi- 

 mentary flagellum, or well developed. The limbs of the 

 peraeon 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 bicuspida (Owen) is beautifully coloured. It has 

 the second antennae well developed. Edotia triloba (Say) 



