BEI'.STON : MOLT.USCA OF GRANGE-OVER-SANDS. I95 



under the same stone on the tops of the walls. In some favoured 

 localities, Fyrnniidula riipestris and Jaminia cylindracea fairly 

 swarmed, and could have been collected by hundreds, yet Jaminia 

 musconan, except in one small spot, seemed extremely rare. Here 

 again closer search ought to reveal this species in other parts of 

 the district. 



Helicella caperata was a fairly abundant snail, and existed in 

 isolated colonies, but why its nearest ally H. virgata should to all 

 appearance be a total stranger to the district seems puzzling, as 

 these two species are more often found together than not. Soil, 

 climate, and other conditions apparently are all suitable, but H. 

 virgata was not present anywhere. 



Such anomalies as these are very interesting, but most difficult 

 of explanation. The presence or absence of a particular species 

 may depend upon some very slight favourable or adverse condition. 

 Of the two species under discussion, H. caperata seems to be some- 

 what more hardy than H. virgata^ as on several occasions, after 

 severe frost, I have found the latter dead in some numbers, while 

 the former appeared to have been quite unaffected by the cold, 

 crawling about actively on the ground, and in no case could I 

 discover one recently dead, though I have taken examples of H. 

 virgata with dead animals immediately after a severe frost. 



Temperature alone I do not consider the cause of the absence 

 of H. virgata in this instance, as the species is recorded for other 

 places in Westmorland, Cumberland, and West Lancashire. Pre- 

 datory birds, mammals, or the prevalence of destructive parasites 

 might account in some way for the non-existence of certain species. 

 Investigations into the causes of anomalies of this character might 

 reveal much that is at present enigmatical regarding the distribution 

 of mollusca. 



Again, one of the things which strikes a collector from the south 

 when visiting the northern districts, is the amazing abundance of 

 the smaller species — the genera Jaminia, Vertigo, Pyramidula, 

 Clausilia, and Vallotiia. It is quite a new and pleasing experience 

 to be able to return from an excursion with, say, a couple of 

 hundred Vertigos, instead of a paltry half-dozen or less, which may 

 reward the conchologist in some parts of the south for a whole 

 day's prospecting. But on the other hand, the scarcity of the genus 

 Helix in some northern localities is disappointing. There are dis- 

 advantages in living at either extreme. 



The freshwater species, too, are few in number and disappoint- 

 ing, at any rate in the immediate vicinity of Grange, owing to the 

 scarcity of streams and ponds of fresh water. The pond in the 

 ornamental grounds did not produce a single species, owing probably 



