Suter. — Species of the Genus Isidora. 267 



by its cylindrical form, the much flatter whorls, and the less im- 

 pressed 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 spelosus from Nelson. 



Type in the Canterbury Museum, Christchurch. 



Potamopyrgus subterraneus, n. sp. 

 Shell minute, subcylindrical, fragile, opaque-white, smooth. 

 Spire pupoid ; apex blunt ; whorls 5, rather convex, the body- 

 whorl more than half the axis ; suture well impressed ; mouth 

 oval, oblique, peristome continuous ; outer lip membranaceous, 

 the specimen being apparently not quite full-grown ; inner lip 

 slightly callous, subvertical. Operculum not seen. Length, 

 2f mm. ; breadth, 1 J mm. 



Hab. The only specimen was obtained by Mr. 

 W. W. Smith, of Ashburton, by pumping water 

 from a well 48 ft. deep. 



It was alive when caught, but upon reaching 

 I f I me the animal was already decomposed. Mr. 

 Smith very kindly presented the specimen to me 

 in February, 1892. I did not describe it then 

 because I hoped to get some specimens with the 

 animal in sufficiently good condition for study. No 

 other specimens, however, turned up. The species is exceedingly 

 fragile, and distinguished, like pupoides, by its subcylindrical 

 form. The nearest allies are egenus and spelceus, but it differs 

 considerably from both. It most likely has been derived from 

 the latter species. 



Type in my collection. 



Art. XVI. — Revision of the New Zealand Species of the Genus 

 Isidora, with Description of a New Subspecies. 



By Henry Suter. 

 Communicated by A. Hamilton. 

 [Read before the Wellington Philosophical Society, September 1th, 1904.] 

 The first short list of species we find in von Marten's " Cri- 

 tical List" (1873), p. 15, consisting of three species: Physa 

 variabilis, Gray ; P. tabulate, Gould ; and Limncea (?) ivilsoni, 

 Tryon (a sinistral shell). The next list, in Hutton's Manual, 

 is more extensive, comprising ten species : Physa wilsoni, 

 Tryon ; P. antipodea, Sow. ; P. gibbosa, Gould ; P. guyonensis, 



