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Potamopyrgus spelæus, Frfid., subsp. pupoides, Hutton.
Potamopyrgus pupoides, Hutton, Trans. N.Z. Inst., vol. xiv. (1882), p. 146, pl. i., figs. D-H. Potamopyrgus pupoides, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii. (1893), p. 620. Potamopyrgus pupoides, Suter, Journ. de Conch., vol. xli. (1893), p. 222.
I have typical specimens from brackish water in the Heathcote Estuary, near Christchurch, and they are so nearly allied to Frauenfeld's spelœus that I find it advisable to give P. pupoides only subspecific rank. It is distinguished from the species
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by its cylindrical form, the much flatter whorls, and the less impressed suture. I have also specimens from Parua Bay, near Whangarei, and from the Onehunga Springs. Those from the latter locality are variable, some corresponding with the type, while others have more convex whorls, and approach the very small form of spelœus from Nelson.
Type in the Canterbury Museum, Christchurch.