GENERAL NOTES. 131 



latter I have, however, as yet only found a single specimen). My 

 experiments will be continued next summer, and I do not doubt that 

 some of the species, at least of the Ostracoda, will reappear in the 

 aquaria, after they have been dried up during the winter." These 

 results are very interesting, and it would greatly increase the value of 

 Prof. Sar's researches in this direction, if samples of mud from the 

 North Island were foi'Avarded to him. I shall be glad to receive and 

 forward any which are forthcoming. The specimens obtained by 

 myself were nearly cubical blocks about four inches deep. — Geo. M. 

 Thomson, Dunedin, 25th April, 1891. 



Idotea lacustris (G. M. Thomson). — This species was originally 

 described by Mr. Thomson in 1879. It is chiefly remarkable because 

 of its occurrence in fresh water as the genus to which it belongs is 

 distinctly marine, and it is the only fresh water Isopod at present 

 known in New Zealand, with the exception of some subterranean 

 forms. It has been taken at different times in the Tomahawk 

 Lagoon, near Dunedin, but it has been a little uncertain whether it 

 lived there permanently in -fresh Avater or only came up when a very 

 high tide rendered communication with the lagoon possible.* It has 

 never been taken in the sea on the New Zealand coasts, but in the 

 British Museum collections there are specimens from Port Henry, 

 Straits of Magellan (Dr. R. P. Coppinger), which are very nearly if 

 not quite identical with the New Zealand species. The exact locality 

 of the Magellan species does not appear to be known, but probably 

 they were marine in habitat. So much was known about the species 

 when Miers wrote his "Revision of the Idoteidte," and though I after- 

 wards described the species in greater detail in my " Revision of the 

 N.Z. Idoteid»" (Trans. N.Z. Inst. XXL, p. 191), 1 was not then able 

 to give any further information as to its distribution. In January of 

 this year, however, Messrs. Wm. Cron and D. Strachan, two enthu- 

 siastic young collectors who have often helped me, brought me some 

 specimens of what appeared to be Idotea lacustris from the Mihiwaka 

 Creek, near the mouth of the Deborah Bay Tunnel, above Port 

 Chalmers, a place perhaps about 200 feet above, sea level. I 

 have since collected numerous specimens from the creek; they 

 are found on the under surface of stones and boulders in the 

 small mountain stream, and undoubtedly are permanent fresh 

 water inhabitants. On examination these specimens were found 

 to differ constantly from the Tomahawk Lagoon specimens in 

 several small points ; thus the eyes are much smaller, the inner 

 antennae are longer and the outer antennre more slender, there 

 is a small depression in the front margin of the head which 

 alters the appearance of the margin, the last segment of the abdomen 

 bears only one pair of sutures instead of two, &c. These differences 

 though small in amount are somewhat numerous, and an examination 

 of a considerable number of specimens from both localities proves 

 that they are constant. They are quite as important as differences 

 that are often held to distinguish species, but in this case it will 

 probably be better and less misleading if the two forms are consi- 

 dered as distinct varieties of the same species. It would be 



* I have found it lately in all parts of the lagoon, quite away from tidal influence 

 and where the water is always quite fresh. — G-. M. T. 



