BRITISH NON-MARINE MOLLUSC A. 



47 



their surroundings would be of no avail whatever against such 

 insinuating and indiscriminate foes as flies. Helix pomatia 

 varies considerably in size, but altitude does not seem to affect 

 it in this particular at all, at least in the Cotteswolds. 



A precisely parallel case is presented to the preceding as 

 regards coloration in respect to the environment in Pomatias 

 elegans, which ranges up to about 900 ft. or thereabouts in the 

 Cotteswolds, and discloses two extreme forms, a dark and a 

 light, the same as the " Koman," the former frequenting the 

 woods, the latter being found more especially, but not exclusively, 

 on the stony, sun-scorched slopes, particularly of the western 

 escarpment. A very difficult puzzle to the tyro of the local 

 paleontology is presented by the occurrence of this shell in a 

 sub-fossilized state, often two or three feet beneath the surface, 

 mixed with Brachiopoda and Marine Mollusca of the oolitic 

 period. They can thus be often seen in situ upon the edge of a 

 stone quarry, and the interesting question arises as to how they 

 came to occur at such a depth below the surface. Well, I have 

 elucidated the problem — at least, to my own satisfaction — during 

 the season by observing how in dry hot summers the surface of 

 the ground cracks in places, reminding me in a small way of the 

 yawning fissures which I witnessed on the plateau of the Cossya 

 Mountains in Assam after the memorable earthquake of June 

 12th, 1897. I have no doubt in my mind that the shells are 

 engulfed or washed into the fissures by storms, the fissures sub- 

 sequently closing, and the shells after the lapse of a number of 

 years becoming eventually fossilized, or partially so. They may 

 be seen in surprising numbers in different places. With them, 

 but as a rule only a few inches beneath the surface, may also be 

 found sub-fossilized shells of Helix nemoralis, Hygromia rufe- 

 scens, Ena obscura, and a few others, but as yet I have observed 

 no extinct post-glacial species of Mollusca among them. 



Most Mollusca in the Cotteswolds, as probably elsewhere, are 

 considerably larger and richer in colour at the lower elevations, 

 especially within the shelter of the woods, becoming smaller and 

 paler in appearance in the higher and more exposed places 

 where greater fluctuations of temperature prevail. This applies 

 especially to Hygromia rufescem, which abounds in many locali- 

 ties up to nearly 1000 ft. Helicella itala also, which is very large 



