CEUSTACEA OF NEW ZEALAND. 253 



or irregular beds of shingle and sand composing tlie plains, at least in the Asliburtoa 

 district. Some of the beds are intensely hard and extremely difficult to pierce with the 

 steel-pointed pipes. After the lowering of the water, Mr. Dolman ascertained when 

 driving the pipes to unusual depths that the pipe frequently entered ' dry-beds,' and he 

 had either to draw up or lower the pipe to tap the water. The deepest well he has 

 driven is 65 feet, and it has continued to give a good flow ever since it was driven. 

 Mr. Dolman states that there is no limit, so far as he knows, to the depth the vrater is 

 found in the plains, although it flows in thinner or shallower streams the lower he sinks. 

 Eeferring to the discoloration of some streams, he informed me that he has found small 

 round particles of clay in the water, and he attributes its discoloration to these floating 

 particles. When sinking open w'ells, Mr. Dolman has occasionally observed the direction 

 and rate at which the subterranean water flows. He estimates its motion at from one- 

 quarter to one-half a mile an hour. One important fact he has several times ascertained, 

 when driving the pipes through the lower and harder beds, is the rising of the w^ater in 

 the pipe to variovis heights from the newly-taj^ped stream. He has known it to rise 

 from 2 fett to 14 feet, and afterwards to remain permanent. There is considerable 

 difference in the work of sinking the various wells — some are put dow^n in a few hours, 

 the pipes driving freely, and others require as many days, and this sometimes with a 

 heavier 'monkey ' at work. These facts can be better studied by an examination of the 

 high sections of the plains at the mouths of the Kangitata and the Ashburton Elvers. 



" The exceptional well I have mentioned, which did not become dry, is driven 27 feet, 

 and is in a low-lying part of the town. Nearly all the pipe-wells originally driven were 

 sunk to various depths, ranging from 15 feet to 22 feet. These, without any exception, 

 became di"y." 



VII. Origin of the Subtekranean Crustacea. 



In considering the source from which the subterranean Crustacea have been derived, it 

 will be well to state first what little is known of the freshwater forms of the Amphipoda 

 and Isopoda found in New Zealand and Austraha. 



In New Zealand only one freshwater Isopod is known, Idotea lacustris, G. M. Thomson 

 [21, p. 263], and this one has no connection whatever with the subterranean fauna. In 

 Australia, however, a species of Fhreutoicm is known, P. mistralis [26], as yet found 

 only on the top of Mt. Kosciusko, about 6000 feet above the sea. In the Amphipoda 

 we have two freshwater species recorded from New Zealand. One, Callioinus fluviatiUs, 

 is very common in almost all running streams of the South Island ; but is also found in 

 various places in Otago Harbour, in water that is quite salt. This species is very abun- 

 dant in the surface-streams of the Canterbury Plains, in the localities wdiere the subter- 

 ranean forms also abound ; but, as I have already pointed out, although it approaches 

 Calliopius subterraneus, it is dissimilar in several respects, and it does not seem at all 

 likely that C. subterraneus is directly descended from it. The other species is Pherusa 

 ccerulea, G. M. Thomson [107, p. 206], found by Mr. Thomson on the top of the Old Man 

 Range, 3000 feet, in Otago, and as yet known from this locality only. I have compared 

 this S2)ecies in some detail with Calliojnus subterraneus (see above, p. 235), and have 



33* 



