HELIX LAPICIDA. 321 



crowded over the sides, and many full-grown speci- 

 mens were also crawling about. As the water from 

 the bore was conveyed pretty directly to the cistern, 

 it was supposed that these mollusks might have been 

 brought up with it; and that they had resisted the 

 effects of the somewhat high temperature to which it 

 had been subjected. But a little investigation sug- 

 gests the probable method by which the spawn of 

 the mollusks is introduced. Some moss and confervae 

 also grow in the cistern, and their sporules may very 

 possibly have been wafted there by the winds. But 

 the most probable method by which the spawn of 

 mollusks would arrive at this cistern, thus placed on 

 the top of the house, is (I conceive) by its becoming 

 entangled about the bodies of water-beetles, and I 

 observed three or four species of these tolerably 

 abundant in it." 



HELIX LAPICIDA.* 



Dec. 8th, 1822. WE found a pollard elm this 

 morning pierced in all directions by the Helix lapi- 

 cida. On tearing away the bark, and portions of 

 the wood, great numbers were observed of all sizes. 

 The tree was so weakened by their attacks, and so 

 much of its substance gone, that a slight wind would 

 have been sufficient to overturn it. These animals 

 appear to eat their way along in the same manner as 

 woodlice, and will soon devour all the internal wood 

 of a tree where they abound. Some of the indivi- 



* Gray's Manual, p. 140, pi. v. f. 51. 



p 5 



