Chilton.- — On Neir Zealand Idoteidte. 19o 



fifth to seventh segments Ijroader and with the postero-Iateral 

 angles shghtly produced. Terminal plates of the operculum 

 with the exterior margin regularly rounded, very finely serrate 

 at the end. Colour, dark-grey. Length, 15mm. ; breadth, 

 7mm . 



In New Zealand this species has been found only in Toma- 

 hawk Lagoon (fresh water), near Dunedin, where it has been 

 taken in considerable abundance. It appears to be identical 

 with specimens, presumably marine, from the Straits of 

 Magellan ; but Miers gives the identification with mucli 

 hesitation on account of the widely-remote locality at 

 which they were obtained. Unfortunately Miers gives no 

 description of these specimens, simply stating that they agree 

 fairly well with INIr. Thomson's description of I. lacustris. 

 However, the figure that he gives would answer very well 

 for /. lacustris, except that it shows one pair of sutures 

 on the last segment of the postabdomen instead of two ; 

 and, judging from the figure, I should say that the Ma- 

 gellan specimens do not differ specifically from I. (acustris. 

 In any case the specimens from the two localities are very 

 closely allied, and would appear to be the remnants of a 

 species probably once abundant and widespread in the 

 southern seas. In that case /. lacustris has probably been 

 preserved in Tomahawk Lagoon owing to its isolation atid 

 freedom from competition with other species, which would 

 appear to have supplanted it on the coasts of New Zealand 

 elsewhere. 



The "dense fringe of very short setae" on the antennae is 

 found in the male only. There is no fringe on those specimens 

 (nine in number) which I know to be females, while it is 

 present in all the specimens (thirteen in number) which I 

 know from other reasons to be males. In all of these it is 

 associated with a similar fringe on the second pair of thoracic 

 legs. In some specimens the fringe is not so well developed 

 as in others, and it seems to be developed first on the antenna; 

 and then on the second pair of legs, for in one or two speci- 

 mens where there is only a slight indication of it on the 

 antennae there is none at all on the second pair of legs. In 

 all probability these fringes are a secondary sexual character, 

 not developed in the males till they are mature, or perhaps 

 developed only during the breeding-season. 



In the antennae the fringe consists of exceedingly fine setae 

 densely packed, and when fully developed is found principally 

 on the last joint of the peduncle, and on the 6-7 basal joints 

 of the flagellum. In the second pair of legs the fringe is 

 formed of setae longer than those on the antennae but of the 

 same kind, and is developed on the inner (lower) surface of 

 the ischios, meros, carpus, and propodos. The setae forming 



