* * **"I have also observed two forms of thoracic plates in the other species (P. bilobus)."*

We have given a figure of the upper portion of Eurypterus remipes (De Kay), after Hall's Paleontology of New York, loc. cit., and by its side the same parts of P. acuminatus. P. bilobus is a very much smaller species than P. acuminatus, and instead of small, simple, and slender antennules,† it has large and strong chele or claws like the great "Seraphim," only on a very much smaller scale. The succeeding organs in P. bilobus are slender and unarmed, whilst those of P. acuminatus are robust and spiny on every joint. The thoracic and tail-plates, too, are quite distinct in shape, and so also is the cephalic shield and the form of the eyes. Feeling as I did the importance of these distinctions, amounting to far more than specific characters, I was much rejoiced at obtaining the independent sanction both of Messrs. Huxley and Salter to place it in a separate genus, adopting for it the name proposed by Mr. David Page— Slimonia acuminata.

The additions which we have been able to make (with the kind assistance of Mr. Slimon) towards the completion of Slimonia acuminata, consist in indicating another thoracic segment; so that the number of body joints is now the same in Pterygotus and Eurypterus, increasing the number of organs from three to five pairs, and demonstrating the true position and character of the thoracic plate. Only one other point of interest remains to be solved, namely, the position and form of the respiratory organs, and upon this subject we are not without good hope.

We must now conclude our brief sketch of this remarkable palæozoic crustacean. Those who wish to enter more fully into their history must refer to the monograph of Messrs. Huxley and Salter, the Quarterly Journals of the Geological Society, Professor Huxley's Lectures on Crustacea (printed in the Medical Times and Gazette for 1857), and Hall's Palæontology of New York for 1859. And all who desire to observe for themselves, should bear in mind that the actual specimens can be seen and studied in our public collections at the British Museum, and the Geological Survey, Jermyn Street.

* The median lobe of plate E, and an almost entire detached thoracic plate of the form figured in woodcut K, were figured in Messrs. Huxley and Salter's monograph; but, not being found in situ, were attributed to the mouth as the conjoined epistoma and labrum.

The antennules of P. acuminatus have their basal joints serrated, so as to form the first pair of mouth organs. The antennules of P. bilobus do not seem to be furnished with serrated basal joints, a most important distinction.

Page's Advanced Text-Book of Geology, 1856, p. 135, f. 3; in compliment to my friend, Mr. Robert Slimon, of Lesmahagow, the discoverer of all the Lanarkshire specimens.

EXPLANATION OF PLATE OF Slimonia (Pterygotus) acuminata, SALTER SP.-Fig. A 1. Carapace of S. acuminata, about onethird natural size, showing the sessile eyes at the angles of its anterior margin (the antennules are not clearly to be seen in this specimen): a, first pair of simple palpi (antennæ); b, second pair of ditto (mandibles); c, third pair of ditto (first maxilla); dd, entire swimming feet, with their broad basal joints, whose serrated edges serve the office of maxilla; e, post-oral plate, or metastoma; f, thoracic or genital plate, covering reproductive organs, and concealing the two first thoracic segments, with its median lobe (g), which was described as the conjoined epistoma and labrum; h, i, k, l, third, fourth, fifth, and sixth thoracic segments, the first and second are concealed beneath the thoracic plate (ƒ); m, n, o, p, q, r, six abdominal segments. The thoracic segments are broad and short, whilst the abdominal are long and narrow; s, telson or tail-joint; h, a, a small portion of one of the thoracic segments highly magnified, showing the characteristic squamose markings upon its surface.

EXPLANATION OF WOODCUTS.-Fig. A. Recent Limulus, "King crab "(female): 1, antennules; 2, antennæ; 3, mandibles; 4, first maxilla; 5, second maxilla; 6 (swimming feet), third maxillæ. Fig. B. Thoracic appendage, covering reproductive organs (a). Fig. C. Antenna of a male Limulus (recent). Fig. D. Foot of swimming crab (recent), Platyonichus ocellatus. Fig. E. Thoracic appendage of Slimonia acuminata. Fig. F. Parka decipiens, supposed eggs of Pterygoti. Fig. G. Head of Eurypterus remipes, De Kay (after Hall's figure), under side, exhibiting the organs of the mouth: a, antennule; b, antennæ; c, mandibles; d, first maxilla; e, (swimming feet) second maxillæ; p, post-oral plate, or metastoma ; m, thoracic appendage; 1, 2, 3, 4, thoracic segments. Fig. H. Upper side of same, showing the eyes, and (b) larval eye-spots. Fig. K. Slimonia acuminata (restored); the letters refer to the same parts as in Eurypterus remipes.

THE MINUTE STRUCTURE OF THE VINEGAR PLANT.

BY HENRY J. SLACK, F.G.S.,

Member of the Microscopical Society of London.

AMONG the minute organisms which puzzle the microscopist the Vibrions and their relatives present great difficulties as regards their structure and classification. Ehrenberg assigned an animal nature to the whole family; but it is far more probable that all are, as some are known to be, vegetable, and perhaps rudimentary conditions of more highly organized plants. In Pritchard's History of Infusoria (fourth edition, p. 187) the results of Cohn's investigations are cited, and we find it laid down by that naturalist that "the Vibrionia apparently all belong to the vegetable kingdom, for they exhibit an intimate affinity with undoubted Algæ." Dr. Burnett is also quoted in the same place to the effect, that "their cell structure and their vital (not voluntary) motion would lead us to infer that the Vibrionia are algous plants, and not animals. This throws light on several common phenomena. One in particular is that the Vibrionia should almost invariably be found in infusions and liquids that contain other Algæ, and especially the common Torula; for I do not remember to have seen the Torula without Vibrionia."

It affords more precision to regard Algæ and Fungi as distinct classes of the sub-kingdom Thallophytes; and the Torula, with which Dr. Burnett found the vibrions associated, is ranked among the Coniomycetous Fungi, and is closely connected with the Yeast and Vinegar Plants.

It is not an easy question to define what is a vibrion, because minute bodies more or less divided into beads may differ widely in their origin, their properties, and their destination. In decomposing solutions objects of this kind invariably appear, and the researches of Pasteur, which are recorded in former numbers of the INTELLECTUAL OBSERVER, and which I, therefore, shall not quote at length, lead to the conclusion that all kinds of fermentations and putrefactions are acts correlative with the growth of these remarkable organisms; and that their life, so to speak, presides over the decay and disintegration of higher animal or vegetable beings, and of the complicated products which they form.

Minute, and usually colourless, thread-like bodies of beaded structure, exhibiting a wriggling or oscillating motion, and destitute of organs (for the alleged filament of bacterium is probably a mistake), are readily recognized as belonging to the vibrion family; but the motion, though a common property,

does not seem an essential characteristic, and we shall only follow good authorities if we admit quiescent objects, which have the same form and exercise analogous functions, as members of the same family.

The usual divisions of vibrions into genera and species, we apprehend, satisfy nobody. Some are larger, some shorter, some divide obliquely, some at right angles to the longer axis. Some are like miniature corkscrews, and so far resemble that pretty confervoid plant the Spirulina. These latter move spirally, and often with rapidity. Others twist and wriggle, others oscillate, and others stand still.

The Micrographic Dictionary provisionally places some vibrions among the confervoid Algæ, and probably all will be distributed between the Algae and the Fungi, the latter seeming most likely, to the writer, to carry off the greatest number.

In Pritchard's Infusoria, p. 531, the genus Bacterium, of Dujardin, is described as characterised by straight slightly flexible threads more or less distinctly jointed, and slow in their movements. In the next page all the species are said to have an active power of locomotion. The activity of motion certainly does not afford ground for generic or specific distribution, and some that are active at one time appear to be quiescent at another. For convenience, Dujardin's division may be adopted, as founded upon external characteristics easily distinguishable in extreme cases, though liable to be more or less confounded in intermediate forms. According to this, first comes Bacterium, the description of which we have just cited. Then we have "Vibrio, either straight or flexuose, with a more or less vivacious writhing movement;" and then "Spirillum, having the form of a corkscrew, revolving on their long axes, oftentimes with great rapidity, but never straight." They are all small bodies; few exhibit the beaded structure with less than an amplification of 500 diameters, and some defy a power of 2000 linear, which leaves them extremely minute in length, as well as in breadth. Ehrenberg constituted six genera of vibrions; and Pasteur, speaking of them, says that they can all exist without free oxygen, and perish in contact with it, if nothing preserves them from its action.* To Monas crepusculum and Bacterium termo he ascribes the disappearance of oxygen from putrefying infusions, and then he tells us the vibrions appear and do their work as ferments, pulling to pieces the complicated organic atoms in a definite way. If this view should be confirmed, it may serve as the foundation for a natural division of the vibrion family: those which live in oxygen and perform one set of functions being distinguishable by action and habit, if not always by appearance, from those which perish in oxygen *See INTELLECTUAL OBSERVER, Sept., 1863, p. 101.