remarkable forms for which the sea of the Antilles is famous. However, although the "Challenger" was not there in person, on her return Sir Rawson Rawson most kindly and liberally placed the finest of his specimens at my disposal for examination and description; and it is through his liberality that I now have it in my power to exhibit the very singular creature which is the subject of these notes. In 1837 M. Alcide d'Orbigny described and figured in the "Magasin de Zoologie," under the name of Holopus, a new recent genus of fixed Crinoids; and as the description of this distinguished palæontologist indicated an undescribed form of great interest, it was speedily reproduced in the "Annales des Sciences Naturelles" and in Wiegmann's "Archiv."

The specimen described by D'Orbigny, which was for a long time unique, was brought from Martinique by M. Sander-Rang. It subsequently passed into the possession of M. D'Orbigny, who described it under the name of H. rangii. D'Orbigny's account was very clear and intelligible, and his determination was fully borne out by his figures; and in Bronn's " Classen und Ordnungen des ThierReichs," published somewhere about 1861, the description and figures are repeated, and a distinct family, Holopidæ, is adopted for the reception of the single species. It is very singular that in the "Historie Naturelle des Zoophytes Echinodermes," by Dujardin and Hupé, published as a volume of the "Suites à Buffon" in 1862, the authors express their opinion that Holopus is not a Crinoid, but some totally different thing, probably a Cirriped, and they profess to have been unable to find D'Orbigny's specimen.

At M. D'Orbigny's death his whole museum was bought by the Jardin des Plantes, and in the year 1867, through the courtesy of M. Fischer, I had an opportunity of examining the original specimen there; and although it was in a very dilapidated condition, I had no difficulty in satisfying myself that it was a true Crinoid of a very peculiar type.

Professor Louis Agassiz called at Barbadoes in the "Hassler' in 1873, and he there saw a second specimen of Holopus in Sir Rawson Rawson's collection. Professor Agassiz intended to have published a full description of the specimen, which was lent to him. for that purpose by Sir Rawson Rawson, but he was prevented from doing so by failing health, and after his death the figures which

he had prepared were published by Alexander Agassiz, with a short note by Count Pourtales, in the "Zoological Results of the 'Hassler' Expedition."

During the last few years three specimens of Holopus rangii have fallen into Sir Rawson Rawson's hands, and from these we will be able to give a pretty good account of the hind parts. All were brought up on fishermen's lines from deep water off Barbadoes. One is very complete in all important points, wanting only the two "bivial" arms, but retaining the mouth-valves. The second is a little larger; it wants the mouth-valves, and again the bivial arms; and with Sir Rawson Rawson's sanction I boiled this specimen down, to figure and describe the separate parts. The third specimen is quite perfect, the arms closely curled in, in their normal position when contracted; but it is very young, only about 8 m.m. in height. Besides the four examples mentioned I am aware of only another, which I have not yet seen; it was shown at the Philadelphia Exhibition, and was afterwards bought by the Museum of Comparative Zoology at Cambridge, Mass.

Holopus is distinguished from all other recent Crinoids by having the basal plates, and the first and probably also the second radials fused together, forming the wall of a tube-like body-chamber, which is cemented beneath to the foreign body to which the Crinoid is attached, by an irregularly expanded calcareous base. This mode of attachment also occurs in the fossil genus Apiocrinus, and in many other forms of the Apiocrinidæ and Cyathocrinidæ, but in these, of course, the cement matter is thrown out at the base of a jointed stem.

The upper portion of this hollow column expands slightly, and its thickened upper border is divided into five strongly-marked facets for the articulation of five arms. Each facet is traversed by a transverse articulating ridge, a little in front of which there is the mouth of the tube which lodges the sarcode axis of the joints, and a little behind its centre there is a somewhat longer aperture which appears to lead into the cancellated structure of the outer part of the wall. There are two large shallow muscular impressions on the surface of the facet on the proximal aspect of the transverse ridge. These facets, I conclude, represent the upper surfaces of second radials, but if so, they differ from the second

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radials of all other recent Crinoids in being connected with the radial axillaries by a true muscular joint instead of by a syzygy. The alternative is that they may be the upper articulating surfaces of the first radials, in which case the next joints may be formed of the second and third radials coalesced, and the syzygy between them obliterated; or, finally, there may be only two radials. There is no trace of any further division of the wall of the column, and the cavity is continued contracting gradually to the bottom. A vertical mark, sometimes a groove and sometimes a ridge, runs from the centre of each articulating facet down the inside of the wall for about two-thirds of the depth of the cavity, when it is lost. The upper border of the cup, bearing the facets, is very irregular in thickness; and in all the specimens which I have seen, including D'Orbigny's, one side of the border is much thicker and considerably higher than the other side, and the three arms articulated to it are much larger than those articulated to the opposite side. There is thus a very marked division into "bivium" and "trivium,” and consequently a bilateral symmetry underlies the radiated arrangement of the antimeres. Singularly enough, the specimen described by D'Orbigny was abnormal, only four arms being developed, a circumstance which no doubt greatly conduced to the doubt with which its determination as an echinoderm was received.

Five "radial-axillary" plates, three larger and two smaller, articulate by corresponding ridges and muscular impressions with the facets of the border of the cup, and each of these bears distally two facets, sloping outwards and downwards, for the insertion of the first brachials. The outer surfaces of the radial axillaries are very gibbous, thrown out into almost hemispherical projections, studded with low tubercles; a deep groove runs up the centre of the inner aspect of the joint, and the two sides send inwards very strong projecting processes, which abut against the corresponding processes of the contiguous joints on either side, and lock into them by a system of corresponding ridges and grooves, so that there appears to be little or no motion between these joints.

The radial-axillaries are each succeeded by two series of about eight similar, thick, wedge-shaped brachial joints, very convex externally, and giving off laterally on each side of the arm alternating, very flat broad pinnules each consisting of about six plate

like joints. The brachials are also provided with strong lateral processes forming a wall on either side of the radial groove, and the sides of adjacent series of these first eight arm-joints are marked with corresponding grooves and ridges, so that, although from the presence of articulating ridges of varying degrees of obliquity, and of muscular impressions; the proximal portions of the arms must be capable of some motion, that motion would appear to be slight. After about the eighth the joints suddenly contract in size and become greatly compressed, and this narrow series extends to about sixteen in number, gradually tapering to the end of the arm.

At the bases of the arms, just above the edge of the cup, five thick calcareous bosses, each composed of the contiguous lateral processes of two radial-axillary joints, project interradially into the cup; and opposite these five rather large triangular plates, meeting in the centre of the disk, form a low pyramid covering the mouth. The oral plates are interradial, and the spaces between them radial corresponding with the arm-grooves.

D'Orbigny described the animal as possessing no anal opening, and this is probably the case, but the material is still too scanty to admit of the full examination of a complete specimen of the skeleton, and the soft parts are unknown.

All the specimens of Holopus which have been hitherto procured are in a very peculiar condition; the thick-walled foot, and massive, somewhat rudely shaped cup and arm-joints are formed of a loose spongy calcified areolar tissue deeply stained with a black-green pigment. There is no appearance of any separate organic matter, either on the outer surface of the skeleton, which is very delicately sculptured like shagreen, or on the articulating surfaces of separated plates; indeed, the whole body is so perfectly hard and rigid that at first sight I thought it might be semi-fossil. It is without doubt recent, but I suspect that the tissues are very imperfectly differentiated, almost protoplasmic. When an arm is put into boiling water it falls into pieces at once, the joints simply coming asunder, and showing no trace of muscular or other organic connection except the axial cords of the joints, which sometimes keep two joints hanging in connection for a little.

Holopus is thus specially characterised among living Crinoids

by the absence of an articulated stem or its representative the centro-dorsal plate; by its viscera being lodged in a hollow peduncle with a continuously calcified wall; and by the absence of an anal opening.

In 1846 Professor Steenstrup described under the name of Cyathidium, a genus of fossil Crinoid from the chalk of Faxoe, which occupies a debatable position between the base of the Eocene Tertiaries and the top of the Cretaceous series. The only portion yet described of Cyathidium is a deep cup or tube with a spreading base of attachment and a thickened rim with articulating facets for five arms. The cup of Cyathidium is somewhat more symmetrical and coralloid than that of the recent West Indian form ; but I see no distinction between them of generic value, and I think we must accept Holopus as another of the links which recent investigations have made so numerous between the fauna of later geological periods and that of the present time.

2. On the Diurnal Oscillations of the Barometer.-Part II. By Alex. Buchan, M.A.

In this communication the author stated that he limited his remarks on the present occasion to some of the more prominent results he has arrived at in the course of this investigation. The paper itself, with the tables, will be submitted when the computations have been finished and thoroughly revised,—a work which must necessarily yet take some considerable time.

It is proposed that Part II. consist chiefly of tables showing the arithmetic mean values of the hourly variations of the different months of the year, with remarks on the more evident conclusions which may be drawn from them. The number of places for which data of more or less completeness have now been obtained exceed 130, situated in different parts of the globe. To these it is proposed to add the results of observations made at sea, chiefly those made by the "Challenger" and "Novara " expeditions.

As regards temperate regions, such as Great Britain, periods of no more than three years' observations give only the broadest characteristics of the diurnal barometric curve. From 20 to 25 years will probably be found to be required to show the