MOLLUSCA NEAR ST. ALBANS. 13 



Clausilia rugosa is perhaps the commonest of those elegantly- 

 shelled molluscs, whose generic name is derived from the presence 

 of an exquisitely contrived shutter, similar in office to an 

 operculum, which automatically closes on the retirement of the 

 animal within the shell, thus affording complete protection from 

 the cold during winter months. 



The larger species, Clausilia laminata, I collected on one occasion 

 from a fallen tree-trunk situated close to the road between Hemel 

 Hempstead and RedViourn ; there were at least thirty specimens 

 herded together within as many square inches in this particular 

 situation. On the first occasion that I noticed them I was 

 unprovided with boxes, and so determined to leave my selection 

 of half a dozen of their number until the following day. In this 

 I was prevented, luit returned after a week had elapsed to find 

 the birds flown, at least from the particular spot whereon I had 

 noticed them. A carefvd search revealed theiu not, and I was 

 turning to go, thinking perhaps that some hungry thrush had 

 forestalled me, when I happened to pull away a piece of loose 

 bark, and there, packed closely together, were my Clausilias, 

 They had doubtless retired thither to gain shelter from the sun. 



This close herding is noticeable, moreover, in the pretty little 

 Cochlicopa lubrica, which also seems to prefer company. On one 

 occasion I counted 47 specimens of this tiny species imder moss 

 in my garden at St. Michael's, in a space not more than a foot 

 square. 



The last example which I will mention in this brief paper is 

 Cydostoma elegans, a species which also well deserves its specific 

 name. I would remind you that this is a typical example of 

 an operculate land mollusc, the operculum being, as you will 

 observe in the specimens exhibited, a highly-developed structure 

 identical with the complementary valve in a bivalve mollusc. 

 This species may be met with wherever the chalk appears on the 

 surface throughout Hertfordshire. But although dead shells 

 may be observed in quantity in such localities, the living animal 

 often escapes notice on account of its habit of burrowing a little 

 distance below the sui-face of the ground. 



Tra}is. Hertfordshire N^at. Hist. Soc., Vol. XIII, Fart 1, February, 1907. 



