NATURAL HISTORY SOCIETY OF GLASGOW. 189 



and a few aberrant forms. Every two excursions have furnished 

 nearly a genus, and forty-seven of the excursions a si^ecies each; 

 the results of seven being nil. The localities may be condensed 

 into twenty-three districts, and in this view each district has 

 yielded about one genus and two species. 



Of the land shells Helix rotundata, Zonites cellaria, and Z. alliaria 

 are most plentiful, and seem equal in numl^er ; then //. hisjnda; 

 then Fupa umhilicata, Clausilia riigosa, and Succinea ])utris; then 

 Cari/chium minimum; then H. nemoralis and its variety hortensis; 

 then H. arhistorum, Z. fiilms, radiatula, and Vitrina pellucida; then 

 Z. crystallinus, and Cochlicopa luhrica. The following also are in the 

 order of their apparent quantities, viz. : H. aspersa, H. lamellata, 

 H. aculeata, Bidimus ohsmrus, H. caper ata, j^ulchella, and rufescens; 

 and last of all ff. fusca and Balia perversa — a single individual of 

 each of these two species being all I could procure. 



Of the fresh- water molluscs there can be no doul)t that Limnaa 

 pieregra is the most widely and plentifully distributed, as it exists 

 in great quantities in almost every canal, ditch, pool, pond, or river; 

 and, what seems inexplicable, varying exceedingly in dimensions 

 in different localities, while to all apj)earance the conditions of 

 its habitat are identical. There is a great paucity of individuals 

 and smallness of size of those Peregrce found in lochs where there 

 are pike, and this seems partly to explain the matter, there being 

 none of these fish either in the Campsie Pond or the Gorbals' 

 Reservoir, where I obtained the largest specimens, those from the 

 latter place being very large. In extent of distribution, number 

 of individuals, and variety of form, the Pisidia probably equal the 

 Peregrce. Physa fontinaUs is found also in the same habitat as L. 

 peregra, and although equalling it in distribution, it is less in the 

 number of individuals. Ancylus fluviatiUs seems to equal Physa 

 fontinaUs in number, but has an entirely different habitat. Bythynia 

 tentacvlata ranks next, and although it be somewhat sj)aringly 

 distributed, yet it is very pletitiful where it occurs; the Paisley 

 Canal teems with it, and at Coats' Works, where the temperature 

 of the water is heightened by the condensed steam from their 

 engine, it could be taken by the bushel. In the Forth and Clyde 

 Canal also it seems very plentiful. Cyclas cornea, Planorbis contm'tus, 

 alhus and spirorbis, also Limiuea palustris, and truncahda, seem 

 pretty equal in number and distribution. Next we have Cyclas 

 lacustris, Amdon cygneus, Uiiio niargariiifer, Dreissena polymorp)ha, 



