Suter. — On New Zealand Mollusca. 257 



From Lake Wakatipu Planorbis corinna and Isidora antipodea 

 were not represented. 



All the Mollusca living in deeper water have much lighter 

 colours, and the test is much thinner and more fragile. With 

 one exception (Corneocyclas hodghini) there is no real deep-lake 

 fauna in these lakes, such as it is known from the subalpine lakes 

 in Switzerland, &c, and this may partly be explained by the 

 poverty of our lakes in molluscan life. Limncea is absent, its 

 place being taken by Amphipeplea, and it is interesting to find 

 this genus represented by one species only. 



The littoral fauna, according to Forel's investigations,* extends 

 to 50-75 ft., and it is therefore evident that many of our known 

 species can live in deeper water without undergoing any great 

 structural change. Generally Unionidce are not found in very 

 deep water. However, Anodonta ponderosa, Pfr., was obtained 

 in 33 ft. in Lake Tschaldyr, in Armenia, by Dr. Brandt, and five 

 species of Unio were dredged in 150-300 ft. in Lake Tiberiade, 

 in Palestine, by Lortet. 



Sphcerium and Isidora have, as far as I know, not been 

 known to live in deeper water, and of Potamopyrgus it is for the 

 first time we get any accurate knowledge of the depths of water 

 in which it may be found living. 



The deep-lake molluscan fauna of New Zealand, as far as 

 Messrs. Lucas and Hodgkin's investigations go, may be con- 

 sidered to be composed of the following species : — 



(1.) Diplodon menziesi, Gray. 

 (2.) ,, ,, svbsp. lucasi, Suter. 



(3.) Sphserium novse-zelandise, Deshayes. 

 (4.) Corneocyclas novozeelandica, Prime. 

 (5.) ,, hodgkini, Suter. 



(6.) Potamopyrgus corolla, Gould. 



(7.) „ ,, subsp. salleana, Fischer. 



(8.) Potamopyrgus badia, Gould. 

 (9.) Amphipeplea arguta, Hutton. 

 (10.) Isidora lirata, Tenison- Woods. 



*Dr. F. A. Forel, "La Faune profonde des Lacs Suisses," 1885. 



17— Trans. 



