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ON THE COEALS OF THE

broader shell. An Oolitic bivalve figured in the same workas Mytilus vicinalis, very much resembles, both in size andform, save that it also is proportionally a massier shell, oneof my smaller specimens. Some of the larger masses of theHelmsdale Isastrea are much fretted by this busy excavator.In one of the smaller fragments of coral on the table we findthe fossil remains of three individual shells that had burrowedin it, and the cell of a fourth; and in the massive corallumbeside it there are no fewer than four-and-twenty of theseexcavations now filled with grit, but doubtless once tenantedby a borer a-piece. If, as is probable, it was living at thetime when the excavators were at work within it, and pos-sessed, what is more questionable, the sense of feeling, itmust have been wofully subject to stomach complaints andfits of griping in the bowels.

Though these lithophagi of the Oolite occur chiefly in thecorals of the period, they are not exclusively restricted tothem. I have found them, though rarely, in Old Hed flag-stones of the conglomerate, and have ascertained that, hadthere been naturalists in those days to differ and dispute, thequestion might as certainly have been raised as now, whetherthe stone-boring shells made their way into the masses whichthey inhabited by mechanical means, or through the agencyof some acidulous solvent The corals, in their recent state,were of course calcareous, and, in consequence, dissolvable byan acid; and the flagstones which the borers usually selectedalso contain a good deal of calcareous earth ; but their pre-vailing material is so largely aluminous and quartzose, thatit seems scarce likely that a mere solvent could have perfo-rated them.

I venture, in conclusion, two general remarks. First, thecorals of the Oolitic system in Scotland , massive in size, andoccurring in some localities in very considerable abundance,resemble in these respects no recent corals of the higher