iSgi.] 



THE BRITISH NATURALIST. 



227 



I will transcribe two short notes on the effects of light on A . ater, the 

 results were as will be seen, quite unexpected. 12th May, 1889, 

 ater placed under glass to try the effect of light on colours, the dark is 

 slaty-black, the lighter fawn, both with light coloured foot fringe." 

 27th June, "The two A. ater placed under glass weigh rather more 

 than igo grains, those still under perforated zinc rather below 100 

 grains, no alteration in color from exposure to light, when separated all 

 were apparently of equal size." 



W. A. Gain, Tuxford, Newark. 



Notes on Decollate Shells. — I have frequently had occasion to 

 observe, when collecting Clausilias in any number, the occurrence of 

 decollate shells. This form of monstrous variation is best known to 

 English collectors in the genus Limncea, and most satisfactorily 

 exemplified in the familiar Biilimus (Stenogyra) decollates L. of the 

 Mediterranean region. 



I am inclined in this particular genus fClausilia ) to account for 

 decollation by a very obvious theory, which probably no one has 

 thought it worth while to ventilate hitherto on account of its triviality. 

 Any conchologist scrutmising an old wall in ordinary dry weather 

 must have noticed how conveniently for his purposes many of the 

 Clausilias project from their coverts, the length of the shell rendering 

 seclusion impossible. This results in the tip of the shell getting 

 bleached (a constant phenomenon), and continued exposure would 

 further tend to disintegration of the affected whorls, and finally to 

 their disappearance, the animal perhaps taking part in this last stage, 

 when his top storey had become dismantled and uninhabitable. Dr. 

 Jeffreys rather vaguely says of the top whorls of Truncatella tviiiicatula 

 Drap. that they are "deciduous at the proper season." This species, 

 however, is marine and invariably decollate at maturity, as is Biil. 

 decollates, in which the loss of whorls must be considerable, judging 

 from youthful examples. 



Anyone who knows Guernsey will remember the moss-grown fort 

 walls above the town of Peterport on the south side. These walls, 

 arid and moistureless to a degree in summer, support large numbers of 

 Balea and Glausilia vugosa in all stages of growths, and here among the 

 latter I have noticed many decollate adults. Both these species 



