Abstract
Examination of the type material and anatomical features of several Australian and New Zealand species of the subgenus Siphonaria, previously considered distinct, indicates they are morphological forms of inadequately described species.
The synonomy and redescription of the external morphology, shell, reproductive system, spermatophore, radula and geographical variation of S. zelandica Quoy and Gaimard, 1833 and S. australis Quoy and Gaimard, 1833 is presented. A new name for S. cookiana Suter, 1909, necessary because the type series contains more than one species, is introduced with shell and anatomical descriptions. Comparisons are made with sympatric cogeners. Shell and radular characters, originally used to describe species, are shown to be widely variable and considerably less useful than reproductive system features for species differentiation.