Sutee. — Species of the Genus Potamopyrgus. 263 



Potamopyrgus antipodum, Gray, sp. (em.). 

 Amnicola antipodanum, Gray, in Dieffenbach's " New Zealand," 

 vol. ii. (1843), p. 241. Hydrobia antipodum, v. Martens, Crit. 

 List N.Z. Moll. (1873), p. 14. Hydrobia antipodum, E. A. 

 Smith, Voy. " Erebus " and " Terror," Zool, vol. ii. (1875), 

 p. 3, pi. i., fig. 19, above. Bythinella antipoda, Hutton, 

 Manual N.Z. Moll. (1880), p. 81. Potamopyrgus antipodum, 

 Hutton, Trans. N.Z. Inst., vol. xiv. (1882), p. 145, pi. i., 

 figs. C, G (except upper right figure). Potamopyrgus anti- 

 podum, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii. (1893), 

 p. 619. Potamopyrgus antipodum, Suter, Journ. de Conch., 

 vol. xli. (1893), p. 221. 



The statement made by v. Martens (I.e., p. 141) that " some 

 specimens are bristly " is not correct. This species has never 

 been found with spines or a carina. 



The diagnosis of the species may be found in Hutton's Manual, 

 and in Trans. N.Z. Inst., vol. xiv. 



P. antipodum is just as variable as most species of the genus, 

 especially in size ; but the conical form, flatly convex whorls, 

 and little-impressed suture are fairly constant characters. 



I have specimens from twelve localities, ranging from Auck- 

 land to Southland. Specimens from Owaka (Clutha) are very 

 small and ventricose, with five whorls only, and measuring 

 4| x 2| mm. Another dwarf form was collected by Mr. E. 

 Murdoch, of Wanganui, on the Waimate Plains. 



The great majority of the specimens are covered with a black 

 coating. It is remarkable that P. antipodum is very often met 

 with in brackish water, and almost without an exception such 

 specimens have the tip of the shell eroded. In some places 

 I saw this species living on Ulva plants. I have specimens 

 from brackish water from seven different localities. 



Type in the British Museum. 



Potamopyrgus antipodum, Gray, subsp. zelandiae, Gray, subsp. 

 Amnicola (?) zelandice, Gray, in Dieffenbach's " New Zealand," 



vol. ii. (1843), p. 241. Hydrobia zelandice, v. Martens, Crit. 



List. N.Z. Moll. (1873), p. 15. Hydrobia zelandice, E. A. 



Smith, Voy. " Erebus " and " Terror," Zool., vol. ii. (1875), 



p. 3, pi. i., fig. 19, below. Bythinella zelandice, Hutton, 



Manual N.Z. Moll. (1880), p. 81. " 



This subspecies is fairly well represented by the upper right 

 figure on pi. i., fig. C, in Trans. N.Z. Inst., vol. xiv. It is dis- 

 tinguished from the species by its somewhat smaller size and 

 more tapering form. Dimensions of type are : Length, 5 mm. ; 

 breadth, 2| mm. It is much rarer than antipodum, but also 

 shows a good amount of variation. 



