NATURAL HISTORY SOCIETY OF GLASGOW. 191 



usually more or less wet with dew, when they can be easily secured, 

 as they then come out of their hiding places to feed. But the best 

 time for procuring land shells, during midsummer, is after a 

 shower that has been preceded by a drought; specimens will then 

 be found easily, which in ordinary circumstances would require a 

 deal of perseverance and miimte searching to obtain. 



On the other hand, the best time for securing aquatic kinds is 

 during dry weather, for two reasons. First, if the weather has 

 been wet for a time, the extra accumulation of water is likely to 

 pass considerably over the bounds of their habitat, and thus pre- 

 vent you from finding them. Second, should it be simply a shower, 

 the disturbance to the surface of the water which the rain-drops 

 occasion is an obstacle to your seeing the bottom, however shal- 

 low, where many of the gasteropods are easily found. What seems 

 to me the best method, therefore, and the one which experience 

 taught me to adopt, is to search for the aquatic sorts during dry 

 weather, and the terrestrial during wet. 



Let me now advert to the third part, viz.. Where to collect, which 

 implies a description of habitat ; and probably I cannot do better 

 than run over the various species in the collection, stating the 

 localities where, and the ckcumstances under which they were 

 found. 



Unio margaritifer, is from a deep pool in the Clyde at the 

 Chemical Works, Cambuslang, which seems literaUy filled with 

 it. I may remark that those specimens which are broad at 

 the beaks, and shorter than usual in their long diameter, are 

 almost always pearl-bearers. This shell is generally found on 

 the banks of pools in clear rivers, such as the Tay, Clyde, Doon, 

 and Teith. 



Anodon cygneiis is from Paisley Canal. I found also a pair of 

 dead valves in Bardowie Loch ; and the banks of the Cart at Car- 

 donald Mills are strewed with broken valves. All my attempts to 

 procure this shell alive were futile, and these specimens I found in 

 a heap of mud recently dredged from the canal. 



Cyclas cornea and lacustris are generally found in company. 

 They are plentiful along the southern boundary of Possil Marsh, 

 and in the canals. I have not found lacustris in the Paisley 

 Canal. They are taken principally at the roots of aquatic plants. 

 Jeffreys says he has not observed 0. lacustris in Scotland, nor seen 

 any notice of its having been found there. 



