. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. of the Ventriculidse of the Chalk. 357 brachial fold which attracted and retained the siliceous fluid in its descent towards the base. Fig. N is a small specimen of this kind, instances which are not uncommon in some places. Fig. 5. PI. XV. represents a specimen which has been longitudinally divided, and has afterwards had the convolutions cleared out by the needle. The white central parts, round the entire edges of which the structure is seen, are the only parts where the tru
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. of the Ventriculidse of the Chalk. 357 brachial fold which attracted and retained the siliceous fluid in its descent towards the base. Fig. N is a small specimen of this kind, instances which are not uncommon in some places. Fig. 5. PI. XV. represents a specimen which has been longitudinally divided, and has afterwards had the convolutions cleared out by the needle. The white central parts, round the entire edges of which the structure is seen, are the only parts where the true central cavity is cut, notwithstanding the section. The depth of the convolutions will be clearly seen. It will also be observed that there are several places where the flattened convolutions do not unite, thus leaving ample means for the free admission of sea-water to bathe the whole inner portion of what is really the external surface of the membrane, though so much surrounded by the overspreading flattened, and thus actually outer, surface. The true inner surface is bathed by means of the access of water through the upper part in the usual way. Specimens vary greatly in size. I have them from an inch to at least eight inches in height. The height to which the flat- tened outer surface is continuous varies in different specimens, being, as might be anticipated, greater in large ones. It is some- times much greater on one side than on the other, a circumstance, however, which, in the living creature, would not at all interfere with the free access of the sea-water, inasmuch as the communi- cation was free all around within and under this expanded con- tinuous surface. The species is found both in Upper and Middle Chalk. 4. Brachiolites annularis. Membrane exceedingly fine in texture, having a primary fold of minute and corresponding depressions arranged in more or less exact quincuncial figure: brachial fold expanding very ra- pidly into a varying number of arms opening into
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