Mollusks. 9013 
numerous channels, generally communicating with each other. In 
each excavation a Helix was lodged, and M. Prévost did not hesitate 
to attribute to the snails the work of excavating the galleries. 
But the credit of first noticing excavations of this nature must be 
given to a countryman of our own. In 1820, the first volume of the 
Rev. John Hodgson’s ‘ History of Northumberland’ was published, 
and, at p. 193 of the second part, there will be found the following 
passage :—“On a sunny bank, called the Ferny-breay, on the north 
of the way to Wallington, and just within the Croft-gate on the east 
side of Whelpington, a stratum of limestone is here and there seen in 
gray projecting masses, the under surface of which is bored upwards 
with cylindrical holes, which are from a line to four inches deep, and 
tenanted, especially in winter, by the banded and yellow varieties of 
the Helix nemoralis. The Limax, while it occupies these cavities 
during the summer, has its fleshy longitudinal disk protruded out of 
the shell, and coiled nearly in a circle on the surface of the stone, the 
summit of its shell hanging downwards; and in this position it pro- 
bably elaborates its den, in the same manner that some of the Pholades 
work their way into clay or wood, or, by a slow but constant process, 
sink and enlarge their cells in the hardest stones.” 
On the 19th of May, 1841, a paper was read by Dr. Buckland, 
before the Geological Society, “On the agency of Land Snails in cor- 
roding and making deep excavations in compact Limestone Rocks.” 
Dr. Buckland, in this paper, first referred to the character of the ex- 
cavations at the Bois-des-Roches, which he had examined during the 
Meeting of the Geological Society of France at Boulogne, in September, 
1839. He then went on to describe perforations in the carboniferous 
limestone on which the Castle at Tenby stands, and assigns them as 
the work of the “same species of Helix as that which had formed the 
cavities in the limestone near Boulogne, and he found within them 
specimens of the dead shells as well as the living. The mode of 
operation by which the excavations were made, he conceived, was the 
same as that by which the common limpet (P. vulgata) corrodes a 
socket in calcareous rocks, and he was of opinion that the corrosion is 
due to-the action of some acid secreted by the body of the limpet or 
Helix.”—(‘ Annals of Natural History,’ 1842). It may be mentioned 
that at the time Dr. Buckland wrote this paper M. Bouchard- 
Chatereaux. was of opinion that the mode of perforation was 
mechanical. It was not until a subsequent period that he adopted 
the chemical theory here advanced by Dr. Buckland. 
. In conclusion, I would call attention to certain points of resemblance 
