MoUusks. 87 



twice the size of any specimen of E. lividus 1 met with. Three fine 

 live specimens of E. sphaera (or esculentus of Fleming) were brought 

 in one evening, and being put into a basin of fi-esh water that their 

 sufferings might be brief, we were surprised to find next morning that 

 their colour was changed ; — spines and crust having become a light 

 grass-green. 



I had expected to make some interesting additions to my cabinet 

 of shells, but in this I was a good deal disappointed. There are, I 

 doubt not, plenty of Mollusca in deep water, but I saw very few upon 

 the shore. Cockles there are in abundance in the sand, as well as 

 Solen siliqua, S. ensis and Mactra subtruncata. 



Rissoa interrupta was common at the roots of the smaller Algae, and 

 Montacuta purpurea, Skenea depressa and Turbo tenebrosus were found 

 nestling at the roots of Lichina pygmaea. I found also imperfect 

 specimens of two rare shells, viz., Pecten nebulosus and Pleurotoma 

 gracilis. 



I was however much gratified by finding on the sand at a low state 

 of the tide, about a score of very fine live specimens of Bulla lignaria. 

 Though not uncommon on the Ayrshire coast, I had scarcely ever got 

 I it there containing the inhabitant. Every conchologist knows that 

 I this Bulla has a calcareous gizzard, of even firmer fabric than the ex- 

 j temal shell. This gizzard is a wonderful piece of mechanism, which 

 ! one would not expect to find in the interior of a very soft mollusk. 

 j Though I had seen it before, I found that T was but imperfectly ac- 

 i quainted with its structure. I thought it was composed of two plates, 



I but I fDund that there were three ; in this respect resembling the giz- 

 zard of the still more delicate Bullaea aperta, though differing consi- 

 derably in form. Two of the plates are triangular, and placed one 



II above the other, like the upper and nether millstones. They are not 

 |; quite flat, but a little concave externally and rather convex internal- 



I ly ; they are bound together with strong cartilage, and on one of the 



II sides of the triangle there is a third valve or plate, giving strength to 

 the cartilage, and keeping the two grinders at some distance, except 



I at the centre, where the convex points meet, and thus leaving, except 

 I at these points, room for the reception of food in the triangular space 



between the two millstones. The food of the Bulla seems to be the 



fry of other shell-fish. Though they seem to indulge very freely as 

 I to quantity, they appear to be wiser than our biped gourmands, for they 



keep to one dish. In every one of the specimens I procured the capa- 

 i cious gullet was filled with the fry of Mactra subtruncata. The gul- 



let was in the form of a corn-sack, quite distended, for each contained 



