Hutchinson. — On Fresh-water Shells. 211 



times, in this way, into very mixed company, lying huddled 

 under the tide-touched salt weed, fringing the countless crab- 

 holes, holding common ground with the coast-loving sea-folk, 

 grey whelks, black auger-shells, and all the fascinating 

 denizens of a swampy littoral. In fact, a mild admixture of 

 salt seems to suit them better than quite fresh water. I have 

 got my largest and most perfect specimens round these sea- 

 creeks ; and, as a rule, the farther up country one goes, and 

 the more rapid the stream, the smaller will the river-snails 

 be. Does not the fact of their nourishing so well in these 

 brackish swamps give a clue to their originally salt-water 

 origin? Curious connecting-links between land- and sea- 

 shells are furnished by two species of the same genus that are 

 common about the Inner Harbour of Napier — Potamopyrgus 

 cumingiani and pupoides. Both plentiful in the lower courses 

 of the Napier Swamp creeks, they shun alike the pure fresh 

 water above tidal influence and the stronger salt of the broads 

 of the Inner Harbour. 



Let me quote a short passage from that delightful book, 

 "The Dispersal of Shells," by H. W. Kew : "Fresh-water 

 forms are said to have been originally derived from the sea ; 

 and, even now, marine auimals in all probability are gradually 

 adapting themselves to fresh water." May we not class these 

 shells as being of those that " are gradually adapting them- 

 selves to a fresh -water existence " ? 



The pond-snails are more fastidious in their choice of a 

 home than the river-snails. They frequent, as I have said 

 before, our lakes and stiller weed-choked streams and pools. 

 The "flask snail" 1 have occasionally found in the back- 

 waters of rapid streams, also Planorbis ; but Bulimus seems 

 altogether confined, in our district at least, to lakes and the 

 still pools of the mud-bottomed creeks of the uplands. 

 Unlike the river-snails, our pond-snails give the salt water a 

 wide berth, pausing inland along our river-banks long before 

 the river-snails have attained the limit of their seaward 

 march amongst the purple wastes of crab-haunted salt weed. 



I have said that our fresh-water mussel is common in many 

 of our lakes. It is, however, rather local in my own district 

 — that is, the country lying between Napier and the Kaweka 

 Eange. Extremely abundant in the small lakes on the 

 Petane side of the Flagstaff Eange, it is absent from many of 

 the lakes farther inland. I find it only in the upper reaches 

 of the before-mentioned Waihau Creek and the Mangaone 

 River. In this it is very unlike its small relative the fresh- 

 water cockle, which is with us almost universally distributed, 

 spreading also with great rapidity. A small pool formed in 

 one of our home paddocks some two years ago by the building 

 of a road-embankment, and isolated from the surrounding 



