LMnd and Freshwater Mollusks. 41 



rule rather than the exception. Among home species the common 

 garden snail (Helix aspersa) is occasionally found sinistral, and 

 its shell then presents a curious cramped appearance. 



The edible snail (Helix pomatia) is not very unfrequent as a 

 sinistral shell in France and Germany, but although most abundant 

 in our chalk districts in England, 1 believe it is doubtful whether 

 any reversed specimen well authenticated as British at present 

 exists. Vast numbers of these shells are brought to the French 

 markets, and I have examined many, but never found a sinistral 

 specimen : this, however, may in some degree be explained by 

 the peasants who supply the markets possibly keeping back any 

 such as curiosities, for I understand they have a superstitious feel- 

 ing that it is lucky to find one. A friend who collected for me in 

 the markets at Corfu, where this shell of very large size is sold in 

 quantities, did not remark any reversed examples. I may mention 

 that this Helix is probably the same species of edible snail alluded 

 to by Sallust, as eaten by Roman soldiers, and was one of the 

 kinds fattened by the Romans in their cochlearia.* 



Besides these reversed shells — deviations from ordinary struc- 

 ture which may be deemed monstrosities — other common helices 

 vary in form to a degree worth observation, the bright striped 

 hedge snails. Helix hortensis and nemoralis, will be found to vary 

 much in the elevation of the spire, and consequent form of the 

 whole shell. The same is the case with Helix virgata, the small 

 banded snail which occurs in extraordinary abundance on dry 

 elevated pastures, downs, quarries, and in the neighbourhood of 

 the sea. A curious series of such shells may be at length collected 

 showing at its extremes a very considerable change of form. Of 

 these species, however, or of any closely allied to them, I have not 

 met with a reversed specimen, nor have I heard of any such found 

 in Great Britain. 



The genus Clausilia is represented in England by four species ; 

 small dark spiral shells of very pretty outline and peculiar internal 

 structure ; and of these the most common is the Clausilia rugosa 

 (called also perversa and nigricans). It is so abundantly distributed 

 that very soon the collector is apt to cease regarding it. I have seen 

 upwards of one hundred packed together under one fragment of 

 beech bark, yet this common species has yielded to me a specimen 

 the most extraordinary I ever met with, or perhaps ever heard of, 

 a shell full grown, perfect in apparent development, but with two 

 mouths; these are placed on opposite sides of the spire, but their 

 position can only be well explained by a diagram. 1 mention this 



• Sail. Bell. Jug. 93. A soldier of Marius gathering by cliance "repentes 

 cochleas," gains a vantage ground unseen, from which he makes a plan of the 

 enemy's camp. 



