THE GEOLOGIST. 



fluid, both 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When the tongue is being withdrawn into the mouth it does not 

 seem to touch the upper jaw, but has full time to be withdrawn 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 Asplenium 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 and its projecting 

 marginal teeth ; the tongue, when I could see it for the fern, was 

 actively assisting. It was a very awkward process, the piece being 

 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. 



By Harry Seeley, 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 mollusca are in the 



