![Thumbnail: [Volume 37, 1904 page 267]](/journals/rsnz/images/rsnz_37/thumbnails/rsnz_37_00_0293_0267_ac_02.gif)
[Read before the Wellington Philosophical Society, September 7th, 1904.]
The first short list of species we find in von Marten's “Critical List” (1873), p. 15, consisting of three species: Physa variabilis, Gray; P. tabulata, Gould; and Limnæa (?) wilsoni, 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,
![Thumbnail: [Volume 37, 1904 page 268]](/journals/rsnz/images/rsnz_37/thumbnails/rsnz_37_00_0294_0268_ac_02.gif)
T.-Woods; novæ-zelandiœ, Sow.; P. tabulata, Gould; P. variabilis, Gray; P. moesta, Ad.; P. lirata, T.-Woods; and P. cumingii, Ad. In vol. vii., P.L.S. N.S.W., Captain Hutton published a list of the fresh-water shells of New Zealand, in which the species of the genus were reduced to four—Aplexa antipoda, Sow.; A. tabulata, Gould; A. variabilis, Gray (= gibbosa, Sow. not Gould, guyonensis, T.-Woods, hochstetteri, Dkr.); and A. moesta, Ad. In 1885 Captain Hutton gave a list of the Limnæidæ in these Transactions, vol. xvii., enumerating Bulinus antipodeus, Sow.; B. variabihs, Gray (= gibbosus, Hutt. non Gould, novæ-zealandiæ, Sow., guyonensis, T.-Woods); B. tabulatus, Gould; and B. moesta, Adams (= lirata, T.-Woods), giving a description and figure of the dentition of the latter. The following species were omitted as not really inhabiting New Zealand: Limnæa wilsoni, Tryon, like Physa pyramidata, Sow., from Australia; Physa gibbosa, Gould, inhabiting New South Wales; and Physa cumingi, Ad., inhabiting Queensland.
In Fischer's Manual, p. 257, we find only two species recorded: Physa guyonensis and P. moesta. With my friend Mr. Charles Hedley, of Sydney, I published in 1893 a “Reference List of the New Zealand Land and Fresh-water Shells,” in which, for the species of Isidora, Hutton's latest classification was chiefly adopted, reducing, however, the species to three: Bulinus antipodeus, Sow.; B. variabilis, Gray (= guyonensis, T.-Woods, novœ-zelandiœ, Sow.); and B. tabulatus, Gould (= moesta, Adams, lirata, T.-Woods). Mr. Hedley added the following species, which for want of literature had escaped the notice of New Zealand conchologists: B. novœ-seelandiœ, Clessin; tenisoni, Clessin; coromandelicus, Dkr.; and hochstetteri, Dkr.
The following year I published, at the request of Mr. H. Crosse, a somewhat more extensive list in the Journ. de Conch., vol. xli., adhering still to three species of Isidora, and reducing Clessin's and Dunker's species to synonyms, as follows: Bullinus variabilis, Gray (= guyonensis, T.-Woods, novœ-zelandiœ, Sow., gibbosus, Hutt. non Gould, novœ-seelandiœ, Clessin); B. tabulatus, Gould (= moesta, H. Ad., lirata, T.-Woods, coromandelicus, Dkr., hochstetteri, Dkr.); and B. antipodeus, Sow.
I have studied now the description and copy of figure, kindly supplied to me by Mr. Hedley, of Physa novœseelandiœ, Clessin, and find it to be identical with Physa lessoni, E. A. Smith, an Australian shell, and it has therefore to be omitted from the list of New Zealand shells. Physa tenisoni, Clessin, is according to the figure a Limnœa, being dextral. Physa hochstetteri, Dunker, was mentioned by Hutton as a synonym of Aplexa variabilis, Gray (antea), but was never mentioned again in his later publications.
![Thumbnail: [Volume 37, 1904 page 269]](/journals/rsnz/images/rsnz_37/thumbnails/rsnz_37_00_0295_0269_ac_02.gif)
When working out the Mollusca 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.