Hutchinson. — On Fresh-ivatcr Shells. 209 



altogether, only the angle remaining to distinguish it from 

 P. antipodarwn, 



Pond-snails (Limn2eid^). 



Of these our four species are Amphipeplea ampulla, Bulimus 

 antipodeus, Bulimus variabilis, and Planorbis corinna. 



Amphipeplea ampulla is common in all our lakes and pools, 

 and occasionally in the still back-waters of our larger creeks 

 and rivers. As its specific name "ampulla" denotes, it is not 

 unlike a flask, the first three whorls being perched in a small 

 spire on the greatly enlarged body-whorl. It is a fragile, 

 translucent, horn-coloured shell, from ^in. to fin. in length. 

 Its fragility probably accounts for its absence from the more 

 rapid reaches of our streams. On the shallow, turbulent 

 shingle bottoms its place is taken by the more solid river- 

 snails. Compared with the river-snails, notice the larger, 

 fleshier body, and the absence of the operculum. 



Bulimus antipodeus, the largest of our fresh-water spirals, 

 is a stronger, more opaque shell than the "flask snail," and 

 has in the adult a longer, narrower spire. The turns or whorls 

 of the shell run in the opposite direction to those of the "flask 

 snail," going from left to right, and so termed a left-handed 

 or sinistral spiral. The "flask snail," as also the great 

 majority of shells, are right-handed or dextral spirals. Note 

 that the whorls are not keeled or angled, a distinction sepa- 

 rating it from the next species, B. variabilis, which always 

 has the body-whorl more or less angled. It seems to me that 

 B. antipodeus merges by transition forms into B. variabilis, 

 but as it is placed as a distinct species I give it as such. 



Bulimus variabilis, as its name denotes, is an extremely 

 variable shell — so much so that some authorities rank its 

 varieties, B. mossta and tabulata, as distinct species. It is 

 distinguished from B. antipodeus by the body-whorl being 

 more or less angled or keeled. Bulimus and Aviphipeplea 

 resemble each other rather closely in the young state, the 

 body-whorl of the former being larger and of the latter 

 smaller in proportion than in the adult shells ; but an unfail- 

 ing distinction is that, whereas the whorls of Amphipeplea run 

 from right to left, a right-handed or dextral spiral, those of 

 Bulimus run from left to right, a left-hand or sinistral shell. 



Planorbis corinna, our last fresh-water spiral, is the solitary 

 member of its genus in New Zealand — and a very small and 

 inconspicuous member too. Of a very different form from the 

 preceding shells, its whorls, instead of being elevated more or 

 less into a spire, all lie on the level, in the same plane — that 

 is, the whorls increasing gradually in size, so that the last or 

 body-whorl is not so large in comparison with the other whorls 

 as in Amphipeplea and Bulimus. In size it ranges here from 

 .14 



