54 Bibliographical Notices. ing these with a hand-lens as they floated in the water, I was struck with the appearance of a Mucedo-Wke. growth with which many of them seemed to be invested. That this, however, was something very different from what it appeared to be, soon be-came evident ; for if the little medusa was touched with the point of a needle, the whole of the flocculent mass would in-stantly vanish. It needed, however, a Tiigher power of the microscope to reveal the true nature of the phenomenon, and show that the apparently parasitical growth consisted of the enormously elon-gated peduncles of the thread-cell-bearing capsules, each of which, as it now proved, had the power, while still cariying the capsule on its extremity, of extending itself to a length which considerably surpassed that of the longer or vertical diameter of the umbrella. While the medusa continued to float undisturbed through the water, the peduncle would remain projected in a straight line from the tentacle, becoming at the same time amazingly at-tenuated ; but on the least disturbance it would become suddenly shortened to less than the one-twentieth part of its length when extended, drawing the capsule back with it in its contraction. During the extended condition of the peduncles, they were seen, with their capsules, to be in a state of constant vibration. This was found to be due to a pencil of long, fine vibratile cilia, which, by the aid of a high magnifying power, could be detected on the summit of every capsule. EXPLANATION OF PLATE II. Fig. 1. Heterocordyle Conybearei, of the natural size, growing upon an empty Buccinum-sheW. Fig. 2. A portion of a colony, magnified : a, a, gonoblastidia loaded with gonophores and extended ; h, gonoljlastidium contracted ; c, po-lypite with the tentacles partially contracted, showing that, when in this state, the tentacles assume a clavate form. Fig. 3. A female gonophore still further enlarged. BIBLIOGRAPHICAL NOTICES. British Conchology, or an Account of the Mollusca which now in-habit the British Islands and the surrounding Seas. Volume If. By John Gwyn Jeffreys, F.R.S., F.G.S. &c. Van Voorst. " Since the publication of the first volume of this work I have made two more dredging excursions to the Shetland Isles, a district which IS by far the most interesting that I know of for the further investi-gation of the British Mollusca. In the interval I revisited the south of France, and also went to the Hanse Towns, Denmark, Sweden, and
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