660 SUBANTARCTIC ISLANDS OF NEW ZEALAND. [Crustacea. 



me that the brackish-water form (var. a) appears to be identical with the Straits of 

 Magellan specimens, which have two sutures on the terminal segment of the pleon, 

 Miers's figure, which shows only one, being incorrect in this particular. Dr. Caiman 

 also says that the fresh-water variety seems to be about as good a species as most 

 species are ; but for the reasons which I have given above I think it less misleading to 

 look upon it merely as a variety which has risen from the brackish-water form, pro- 

 bably comparatively recently. Unfortunately, it is not known if the Patagonian 

 specimens are from salt, brackish, or fresh water ; but the facts now before us seem 

 to show that Idotea lacustris is a species widely distributed on subantarctic shores, 

 and is to be found chiefly in brackish water, but has in more than one place ascended 

 fresh-water streams to a considerable height, and become slightly modified, in accord- 

 ance with the different conditions to which it was exposed in these situations. 



Genus Paridotea, Stebbing, 1900. 

 Paridotea, Stebbing, South African Crust., pt. i, p. 58, 1900. 



Distribution. — Southern seas. 



I have followed Stebbing in adopting the genus Paridotea, though one of the 

 main characters on which he founded it (the amount of segmentation indicated 

 in the pleon) is subject to variation even within the limits of a single species, as 

 I have elsewhere shown,* and the custom of establishing a new genus for a single 

 species, unless done after full review of allied species, is apt to lead to needless 

 complication, by making necessary the creation of other genera on equally small and 

 unimportant points of structure. 



Paridotea ungulata (Pallas). 



Oniscus ungulatus, Pallas, Spicil. Zool. Fasc, ix, p. 62, pi. iv, fig. 11, 1772. 

 Idotea ungulata, Miers, Journ. Linn. Soc, Zool., xvi, p. 52, 1881 ; 

 Chilton, Trans. N.Z. Inst., xxii, p. 196, 1890. Paridotea ungulata, 

 Stebbing, South African Crust., pt. i, p. 53, 1900, and pt. ii, p. 56, 

 1902 ; Chilton, Trans. N.Z. Inst., xxxviii, p. 272, 1905. 



One specimen was taken in Carnley Harbour by Professor Benham ; it was 

 taken on Ulva, and was, like the Ulva, of a bright-green colour. 



The species is widely distributed in the southern seas, being known from New 

 Zealand, South Australia, Chili, Rio Janeiro, South Africa, and the Indian Ocean. 



In the paper last quoted I have given some account of the sexual differences in 

 this species. 



Suborder ONISCOIDEA. 



[ Fam. Trichoniscidae. 



! Genus Trichoniscus, Brandt, 1833. 



Distrihution. — World-wide. The section of the genus to which the following 

 species belong is confined to lands in the Southern Hemisphere. 



Trans, N.Z, Inst., xxii, pp. 197, 199, and 201. 



