Tn Lake Titicaca, South America, about 13,000 feet above sea- 
level, there are found several species belonging to the genus 
AU or chesty a littoral genus which had previously yielded but one 
or two authentic fresh-water species.* 
I have recently taken Idotea lacustris , Thomson, in Mihiwaka 
Creek (near Port Chalmers, N.Z.), a rocky mountain stream run- 
ning from Mount Mihiwaka (about 2,000 feet) to the sea ; the 
place where I took the specimens was, however, perhaps not more 
than 200 or 300 feet above the sea. Before this the species was 
known only from Tomahawk Lagoon, a fresh-water lagoon quite 
close to the sea. Almost all the other species of Idotea are marine. 
It is quite possible that diligent search in our mountain lakes 
and streams would reveal other species that have been similarly 
preserved in these situations. 
From the discussion given below of the position of this new 
species among other Isopoda, it will be seen that it does not fit 
into any of the usually recognised families of the Isopoda, and 
that it will therefore be necessary to form a special family for its 
reception. This family, which appears to approach more nearly to 
the A sdlidcc than to any other, may be provisionally defined as 
follows: 
Family PM REATOTCI 1 )/E. 
Body sub-cylindrical, more or less laterally compressed. Man- 
dibles with a well developed appendage. Legs distinctly divided 
into an anterior series of four, and a posterior series of three. 
Pleopoda broad and foliaceous and branchial in function, hut not 
protected by an operculum. Abdomen large, of six distinct seg- 
ments. IJropoda styliform. 
Genus Piireatoicus, Chilton. 
[Transactions New Zealand Institute, XV., p. 89.] 
The following is the original diagnosis that T gave for this genus 
when T had only the one species P. typicus before me. [twill 
include our present species without further modification. 
Generic diagnosis . — “ Body long, sub-cylindrical, laterally com- 
pressed. Upper antenna short, lower long, with flagellum. Man- 
dible with an appendage First pair of legs subchelate, others 
simple ; first four pairs articulated to body at the anterior ends of 
their segments and directed forwards, last three articulated at 
posterior ends of their segments and directed backwards. Abdo- 
men long, of six distinct segments, last joined to telson. Sixth 
pair of pleopoda biramous, styliform. Telson large, subconical.” 
# Bulletin of the Museum Comparative Zoology, Cambridge, Vol. III. 
No. 16, p. 361. 
