151 



Til Lake Titicaca, South America, about 13,000 feet above sea- 

 level, there are found several species belonging to the genus 

 Allorchestes, a littoral genus which had previously yielded but one 

 or two authentic fresh-water species.* 



T have recently taken Idotea lacustris, Thomson, in Miliiwaka 

 Creek (near Port Chalmers, N.Z.), a rocky mountain stream run- 

 ning from Mount IMihiwaka (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 stiearas 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 tit 

 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 AaeUidce than to any other, may be provisionally defined as 

 follows: 



Family PHREATOICID^. 



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, but not 

 protected by an operculum. Abdomen large, of six distinct seg- 

 ments. Uropoda styliform. 



Genus Phreatoicus, Chilton. 

 [Transactions New Zealand Institute, XV., p. 89.] 



The following is the original diagnosis that I gave for this genus 

 when I had only the one species P. typicus before me. It will 

 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 /o?«' 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. 



