44 
THE GEOLOGIST. 
fluid, botli at the head and all along the foot, but have entirely failed 
to detect any pink colouring denoting the presence of an acid. 
When the tongue is being ^Yithd^awn into the mouth it does not 
seem to touch the upper jaw, but has full time to be withdrawn 
before the upper jaw closes ; indeed it does not seem to close en- 
tirely, the downward movement appears to be more connected with 
the action of swallowing than made for the purpose of meeting the 
tongue. On putting a little water to the animal, of which it seems 
to be very fond, the drinking action is seen to be different. I do 
not think the tongue is protruded, but there is a rapid movement of 
the whole mouth until the supply fails, when the tongue again comes 
into play. 
Desirous of witnessing the usual mode of feeding, I placed some 
slices of the fronds of Asiolenium marinum on the glass. The 
H. aspersa attacked and devoured this very greedily. It was curious 
to watch the upper jaw, before so inactive, now making such stre- 
nuous efforts to get it into the mouth ; the latter was distended to a 
gape, displaying the interior brown ribs of the roof audits projecting 
marginal teeth ; the tongue, when I could see it for the fern, was 
actively assisting. It was a very awkward process, the piece beiug 
too big and difficult to manage. 
From these observations it appears certain that the mouth has two 
distinct actions — the licking and the biting action. It also appears 
equally certain that lime is needful to the animal, and is taken in 
the same way as food ; from which I infer that the Helices, when 
they are occupying the cells in the limestone rocks, abrade the walls 
with the tongue for the purpose of getting the lime (and that they 
hold this instinct in common with the rest of their species), hence 
the irregularity, dissimilarity, deformity of those cells much fre- 
quented by them ; but that the original cellular form of the erosion 
is due to some marine mollusk of the Glacial period. 
A HELP TO THE IDENTIFICATION OF FOSSIL 
BIVALVE SHELLS. 
Br Haeky Seelet, F.G.S., 
Woodwardian Museum, Cambridge. 
Lamellibranchiate shells are the most abundant fossils of most 
rocks. Numerous in genera, and prolific in species, they are multi- 
tudinous in individuals, and the specimens vary. The study is not 
easy. It has little of the poetry of many other branches of natural 
history, and has naturally received less attention. But in each sub- 
kingdom specially, no less than in the animal kingdom generally, the 
law holds good that the lower the organization the longer is the du- 
ration in time. And so, important as the higher moUusca are in the 
