Suter. — Species of the Genus Isidora. 269 



When working out the Mollusea collected by Mr. K. Lucas 

 in New Zealand lakes, I had the same experience with Isidora 

 as with Potamopyrgus : the lumping of species had been carried 

 on too far. I do not wish to exonerate myself from blame, and 

 I freely confess that never before have I made a careful study 

 of our species of Isidora, as their great variability makes it 

 extremely difficult to decide the limit of species and subspecies. 

 A good collection of specimens from various localities, besides 

 plenty of time and patience, is necessary for the successful 

 study of these fresh-water molluscs. Specimens from over 

 twenty localities were used to write the present revision, and I 

 hope that it will form a sound basis to work upon. 



Physa variabilis was the first species described by Gray (in 

 " Dieffenbach's Travels," vol. ii. (1843), p. 248)/ The very 

 short diagnosis, unaccompanied by a figure, has in my opinion 

 been the curse of New Zealand conchologists. From the many 

 species judged to be synonyms of this unfortunate variabilis 

 it can be gathered that no one ever knew what Gray's species 

 is — perhaps not even Gray himself, for his diagnosis fits nearly 

 all our species. So it has become a regular olla podrida : all the 

 forms that did not fall under a recognised species were simply 

 labelled " variabilis, Gray." I have come to the conclusion 

 that as long as we retain this species there is no possibility of 

 classifying our various forms of Isidora correctly, and I reject 

 it as insufficiently described, unfigured, and embracing perhaps 

 several distinct species. 



Genus Isidora, Ehrenberg (1831). 



Synonyms : Diastropha, Gray (1840) ; Ameria, H. Adams 

 (1861) ; Glyptophysa, Crosse (1872) ; Pyrgophysa, Crosse (1879) ; 

 Physastra, Tapparone Canefri (1883). 



Animal without the produced and reflected mantle-lobes of 

 Physa ; radula Limnaeidian, approaching Planorbis rather than 

 Limncea ; central tooth bicuspid, cusps rather blunt, base 

 square ; laterals tricuspid ; marginals serrate. Laterals about 

 6-10, marginals about 25-33. Number of rows varying between 

 140 and 220. 



Shell sinistral, resembling that of Physa, acuminated or 

 gibbous, smooth or keeled ; texture somewhat thick, covered 

 with a deciduous epidermis ; columella strong, often reflected, 

 umbilicus sometimes very wide and deep. 



Distribution : Australia, Tasmania, New Zealand, New 

 Guinea, New Caledonia, Fiji, Tonga, Africa (north, north-east, 

 west, and south), southern France, Spain, and all countries 

 bordering the Mediterranean. 



Ameria was proposed for Physa? with keeled whorls. The 



