152 
weathered burrows of departed Pholades, but have been and 
are being hollowed out by Helices, the principal, if not the 
only agent, being H. adspersa. A specimen of the burrows 
was exhibited. 
Mr SEELEY described Helices which he had seen at Charlton 
(Kent), which hollowed themselves small depressions in cracks 
in the chalk. Also Pholas burrows which he had seen in soft 
limestone in various parts of the south of England. These 
were very unlike the specimen handed round. He thought, 
however, that although Mr Bonney had admitted it, the bur- 
rows need not have been effaced by submersion, giving in- 
stances of their preservation. 
Mr Bonney replied that he thought that the Carboniferous 
limestone if immersed must have been weathered, and pointed 
out that most of the instances adduced by Mr Seeley were in 
harder rocks. 
Mr FIsuER said that the holes not being vertical to the sur- 
face was fatal to their being Pholades, but quoted the opinion 
of Mr Pengelly, who thought they were made by some marine 
mollusks. 
(2) Tidal phenomena investigated according to the laws 
of fluid motion, taking into account fluid friction. 
By Mr Rours. 
Professor ADAMS made some remarks on the difficulty of the 
subject. 
The ASTRONOMER RoyaL made a remark upon Laplace’s 
theory of the tide. 
Professor CHALLIS stated the mode in which he should wish 
the problem attempted. 
(3) Mr FisHer exhibited a flint implement which he had 
found on a heap of gravel which was stated to have been 
dug at Chesterton. 
