122 Transactions.—Zoology. 
this colony, and it may therefore help to swell the alreag 
long list of shells erroneously ascribed to New Zealand. y 
4, Gundlachia, sp. Plate XIV., figs. 1-6. 
About two years ago I found in the River Avon, below the 
outflow of the Horseshoe Lake, a minute ancyliform shell, 
which I could not separate from Ancylus woodsii, Johnston 
(figs. 1, 2), from Tasmania. I then found only empty shells, 
but further collecting furnished a good number of them alive. 
On examining the shells I found, to my great surprise, that in 
several of them the base was more or less closed by a septum, 
as it is found in the Tasmanian Gundlachia (fig. 3). On con- 
sulting Johnston’s papers on the T'asmanian fresh-water shells 
I found the statement that his Ancylus woodsii has “the 
animal and teeth almost similar to Gundlachia peiterdi” (}), 
and that in the young state the shell of Gundlachia resembles 
the common Ancylus. I compared the dentition of our shell 
with that of a Gundlachia from Ohio, and there was almost no 
difference ; therefore the shell from the River Avon must be 
considered as a Gundlaciia. Figs. 4 and 5 show the form of 
jaw and teeth. The shell, on attaining its full development, 
will, no doubt, resemble the Tasmanian G. petierdi, but I 
have not yet succeeded in finding it. According to my own 
observation, and information received from Tasmania, Gund- 
lachia seems to attain but seldom its full development, but 
grows and dies mostly in its ancyliform shell, without even 
attempting to form a septum. This is shown by the fact that 
here, as well as in Tasmania, Ancylus woodsiiis abundant, and 
Gundlachia is rare in the same locality. 
Professor Hutton told me that this Guwndlachia in the 
River Avon might possibly have been introduced from Tas- 
mania on aquatic plants used for packing trout-ova. This 
may be, but [ rather doubt it, for the following reason: I have 
not found yet the shell in question from the outflow of 
Horseshoe Lake upwards to the fish-hatching establishment, 
a distance of several miles, but only in that outflow and down- 
wards from its disemboguement in the River Avon. Very 
likely it is living in that lake, and was brought down to the 
river when the canal was cleared from weeds. The lake is not 
easy of access, and 1 have not had an opportunity of exploring 
it. The question whether it is an introduced form or not 
can only be settled with certainty when it is found in & 
locality where the above-mentioned mode of introduction is 
out of question. | 
The fact of Gundlachia occurring in New Zealand would 
not be astonishing at all, for we have, besides some genera 0 
fresh-water shells, of the land-shells the sections Flammulind, 
Gerontia, Phacussa, Allodiscus, Thalassohelix, Phrignathus, 

