Mr. Galloway has done good service in his persevering study of the agency of coal dust in producing colliery explosions.

He has completely refuted the old-established notion that they are simply due to the combustion of the hydro-carbon gases to which the miner gives the name of fire-damp." Mr. Galloway has demonstrated clearly that fine coal dust stirred into ordinary air forms a mixture having fearful explosive energy. The only question which he leaves debateable, is whether a destructive colliery explosion may be due to this alone, or whether an initial explosion of fire damp always occurs.

That such initial explosion, by stirring up the coal dust otherwise lying dormant, and at the same time igniting it, may be in many cases operative is not to be doubted; but the very practical and very serious question, of whether a pit free from outbursts of carburetted hydrogen may nevertheless be liable to explosions if dry and carelessly worked, still remained open. Mr. Galloway contends that the dust alone is dangerous; others have denied this, notably so MM. Mallard and Le Chatelier in their report to the French Commission du Grisou. Since this a Prussian Fire Damp Commission has been appointed, and has investigated the subject very thoroughly, their results confirming those of Mr. Galloway.

The subject is of great and growing importance. We are rapidly exhausting our old coal seams, and continually going deeper and deeper to supply the voracious demands of our blast furnaces, gas works, wasteful fire-places, &c., and as we get deeper, we come upon dry workings, where, unless special precautions are taken, every shot stirs up a cloud that may contain particles fine enough to produce a local explosion, the which stirs up another cloud to explode in like manner, and so on to fearful results, even in a pit where naked candles may be carried with safety if the air is not violently agitated. The practical bearing of this upon the kind of precaution demanded is self-evident. The source of danger being so different from that of fire damp, the precautions must be modified accordingly.

The commercial results of sewage farming are usually very discouraging. This however has not been the case at Forfar, where, according to the published accounts, a field of 38 acres, which cost £3,600, or £94 per acre purchase money, has yielded a profit, the total cost of working being £220 15s. including horse labour, manual labour, seed and repairs, and auctioneer's commission. The receipts were £509 12s. 6d. leaving a balance of £288 17s. 6d. or 8 per cent. on the capital outlay. This however does not include any management expenses, but supposing a capitalist to have undertaken it, and managed his own business and thereby saved the £24 5s. 2d. charged for auctioneer's commission, he would have obtained a return of nearly 9 per cent. with very little trouble. We appear to be within measurable distance of

S. calcitrans enters our houses, and, by its persistent and aggravating attacks on mankind, does much to destroy the equilibrium of the best of tempers. It is commonly known as the stable fly, but is not at all disinclined to pay attention to oxen, &c. So similar is it in general outward appearance to the ordinary house-fly, that, unless special attention is directed to the mouth organs, it may easily be mistaken for Musca domestica, but while the latter is comparatively an inoffensive creature, the former is an unmitigated nuisance; in fact, the only redeeming point about it is of a purely negative character. Possibly by stimulating the attacked party to take some exercise to rid the pest, it may do some good, but the benefit thus derived is more than counterbalanced, if a quiet after-dinner nap has been contemplated. The proboscis is cylindrical, with an enlargement near its point of attachment to the head. Unlike the Muscidæ, it is incapable of being withdrawn, but always projects from the head downward and slightly forward. It is chitinous, black, hard, and beautifully polished. Under the microscope, about three-fourths of the circumference is seen to be thickly set with very delicate' transverse striæ, and

a fourth part at first-sight apparently quite devoid of any marking. By careful manipulation with a couple of needles this may be withdrawn, and will be found to consist of two distinct parts, an outer one, or sheath, through which the enclosed needle-like organ freely moves. When the proboscis is in its natural condition, these parts are seen to enter, and are capable of being moved within the cylinder, which extends for a short distance towards the end of the proboscis. A reference to figure 99 will give

and necessary to some extent if we desire to comprehend the action of the mouth.

The free ends of these organs are very thin and delicate, and quite inadequate as a means of inflicting a puncture. Their use undoubtedly is to convey the liquid aliment to the cesophagus by constantly sliding the parts within each other, on the same principle as that employed in some instances for lubricating machinery by means of the needle lubricator, which may be familiar to many.

some idea of the two parts referred to, the main portion of the proboscis being omitted.

a is the sheath (Labrum) carrying the needle, b (Lingua) in its concavity, while the convex side being outward completes the cylindrical outline of the proboscis. The aperture at the extremity of the sheath agrees in size, and comes into close proximity to the mouth, or rather that part of it in which the organs of dentition are situated, and to which these notes are chiefly intended to refer; but the whole organ is so full of interest I have been led to make these remarks as bearing in some measure upon the subject,

The enlarged portion of the proboscis is liberally provided with muscles, and from these tendons extend down to the mouth; they are very numerous, sufficiently so to supply individual movement to the teeth and other organs therein contained.

In order to display these organs a different mode of procedure is necessary to that employed in Muscidæ. The end of the proboscis must be cut off, and the point of a very fine knife inserted in the opening and laid open, similar to what is done to display the gizzard of a beetle. The operation is well calculated to test the patience of the operator,

and many failures will occur before a satisfactory view will be obtained, unless singularly fortunate or proficient.

The teeth are of two distinct types, and associated with them are other organs to which reference will be made. The primary set are stout and admirably formed for puncturing the skin of the victim selected. They are five in number (dealing as heretofore with one half of the mouth), each of these carries one rather small point or denticle, and, in addition, they are very finely serrated, three on one side only, the two central ones on both sides, but it requires a high power to see this distinctly. In this respect the figure is slightly exaggerated for clearness' sake. Immediately behind these teeth, and situated near to their apex, is a set of short curved appendages, a pair being allotted to each tooth. They are quite opaque and uniform in thickness throughout. Their use appears to be for maintaining hold while the other instruments do the cutting and wounding. Next follow a set of sabre or lancet-shaped teeth, very fine at the points, and by the lightness of colour, delicate in structure, but, nevertheless formidable in number for the size of the mouth. These are the organs for making an incision. When this has been accomplished, the small hooks are inserted, and the primary set soon completes the work. The margin of the mouth is very thickly set with strong hairs, each springing from a well-defined base, apparently capable of movement. The integument is quite opaque, but near the margin assumes a tesselated appearance, the original cellular structure being preserved, the cells are partly filled with pigment, thus leaving the margins well defined.

It will be observed there are no pseudo-trachea present as in the Muscidæ, and as these play an important part in the collection and conveyance of the food, their absence is fully provided for in the organ I have attempted to describe.

If these creatures are plagues when alive, to the microscopist, they are in death doubly so, at least with regard to their mouth organs. Small, hard, and very brittle it is extremely difficult to obtain a fairly representative mount, but patience and perseverance will accomplish much. In this case it has done a little to explain the wonderful contrivance employed to replenish the larder of this little

creature.

SLUGS BITING.-It is stated by Rimmer that Testacella will "bite savagely." I have never succeeded in making it do so, but the other day on handling a large black specimen of Arion ater the animal at once seized one of the folds between the fingers of the hand on which it was placed. The rasping action could be distinctly felt, and after he had been allowed to operate for about a minute the skin was seen to be abraded.-W. Gain, Tuxford.

CHAPTERS ON FOSSIL SHARKS AND RAYS.

THE

By ARTHUR SMITH WOODWARD.

V.

SPINACIDE.

HE Spiny Dog-fishes and their allies form a large family whose paleontological history appears to begin with the deposition of the Lias. So far as is known, Palæospinax, from the Lower Lias of Lyme Regis, is the fore-runner of the race, and the earliest example of a living genus is Spinax primavus, from

the Cretaceous rocks of Mount Lebanon.

Exceedingly perfect specimens of Palæospinax have been discovered in the well-known Liassic fishbeds of Lyme Regis, and by a study of these remains Sir Philip Egerton has been able to elucidate the structure of the genus ;* space, however, prevents us from entering far into the anatomical details, and it is only possible to glance at one or two of the most prominent features. The ordinary length of the shark being not much more than eighteen inches, the teeth are very minute, and the use of a lens is necessary to reveal their characteristics. They are remarkably Hybodont in shape, but a great difference exists between those of the upper and lower jaws, and there is also considerable variation even in the dentition of the same jaw; fig. 101 represents a tooth from the anterior part of the upper jaw, and fig. 102 a lower tooth of corresponding position. The dorsal fin-spines (fig. 105, A, B) are likewise of small size, and their external surface is smooth, exhibiting no ornament except a few scattered tubercles and indistinct lines of growth at the base of the exposed portion it is interesting to notice that the anterior spine (A) is smaller, stouter, and more recurved than the posterior (B)-the reverse of what occurs in Hybodus and Acrodus. The slender body is covered with fine shagreen, and the fins appear to have possessed strong supporting rays of cartilage; and, although the second dorsal fin almost corresponds in position with that of Cestracion, there are indications of the anal being merged with the caudal (according to Egerton), and this is a special character of the family now under consideration.

The history of Drepanephorus affords a typical example of the slow but steady progress of palæontological knowledge. In 1822, some spines and vertebræ from the Chalk of Lewes were referred by Dr. Mantell to the Teleostean "File-fish," Balistes. In 1838, Prof. Agassiz showed that the fossils in question really belonged to a shark, and considered them to indicate an extinct species of the living genus, Spinax, which he designated S. major. Twelve years later, Sir Philip Egerton described

Mem. Geol. Surv., Dec. XIII., 1872, Pl. VII.; see also Quart. Journ. Geol. Soc.," vol. xxix., 1873, p. 420; and "Ann. and Mag. Nat. Hist.," [5], vol. vii., 1881, pp. 429-432.

some scattered teeth from the Chalk, under the name of Cestracion canaliculatus, because they seemed to differ but little from those of the recent Cestracion, except in their smaller size and the possession of a minute channel passing obliquely through the root of each. Three years after this, in 1853, the same ichthyologist announced the discovery of a specimen proving the teeth and spines to belong to one fish; and in 1872 Sir Philip, also, published detailed descriptions of all the more important specimens then available, and proposed the generic name by which this Selachian is now known.* Fig. 106, A, B, are drawings (half nat. size) of the first and second dorsal fin-spines, which are only marked by lines of growth and do not appear to have been very deeply implanted in the soft parts; and figs. 103, 104 represent an anterior and posterior tooth, the former quite prehensile, and the latter adapted for crushing, as is the case in the front and back teeth of Cestracion. D. canaliculatus is the only species of the genus at present recognised, and its remains occur chiefly in the Chalk, although other English Cretaceous deposits have yielded a few fragments.

46

RHINIDE.

Our object in this series of articles being to dwell chiefly upon those Selachian fossils that most commonly come under the notice of English collectors, and to summarise the results of the latest researches relating to such, a passing notice will suffice for the small, but interesting family of 'Angel-fishes" and "Monk-fishes." None of their remains are known to occur in British strata, and the Lithographic Stone (U. Oolite) of Bavaria and France appears to be the only Continental deposit yielding examples of importance. These have been referred to the living Rhina (= Squatina) and the doubtfully distinct genus Thaumas: though the gillopenings are lateral, the general form of the body is much like that of the Rays, and there are no dorsal spines.

PLEURACANTHIDE (XENACANTHIDÆ).

This is an extinct family, of which much yet remains to be learned. It comprises the various forms that have been described at different times under the generic names of Pleuracanthus, Diplodus, Orthacanthus, Xenacanthus. and Triodus, and which it is now almost universally agreed to unite under the first (the earliest) of these terms. Triodus is undoubtedly identical with the previously-described Xenacanthus, and there is no doubt, likewise, that this is the same as Pleuracanthus. The chief disputed point is, whether Pleuracanthus and Orthacanthus really differ generically, or merely specifically,

* Mem. Geol. Surv., Dec. XIII.

and the most recent contribution* to the subject, by Mr. J. W. Davis, of Halifax, seems to show that the latter is most probably the case.

The ordinary fossil remains of this family met with in Britain, are confined to Carboniferous strata, and present themselves in the form of detached spines (called Pleuracanthus and Orthacanthus) and teeth (known as Diplodus), but the Continental specimens, to which we shall shortly refer, are much more complete and occur chiefly in the Lower Permian. The spines are long, usually straight, and tapering to a point, with a smooth or finely striated surface, upon some part of which are arranged two longitudinal rows of denticles; they much resemble the spines of recent Rays in external shape, but differ from those of such as Trygon and Myliobatis in not being solid, but possessing a hollow cavity which opens at the base. Fig. 107 represents a typical example of the Pleuracanthus spine, half the natural size, and the diagrammatic transverse sections, figs. 108, 109, show the difference between this and the form originally termed Orthacanthus; the latter, it will be observed, is much more cylindrical than the former, and the rows of denticles are placed close together along the back, instead of far apart along the sides, but in the paper already mentioned, numerous intermediate forms are described, which demonstrate that these are only the two extremes of a nearly continuous series.

The little bodies known as Diplodus (fig. 110) consist of a thick bony base, upon which are fixed two comparatively large diverging denticles, with a smaller denticle and a little flat-topped or rounded boss rising between. They occur not unfrequently at many Coal Measure localities, and considerable numbers are sometimes met with in association.

Agassiz originally described them as teeth, and this scems to be the view now generally accepted, but some paleontologists have expressed the opinion that they are simply dermal tubercles analogous to the prickles of the "Thornback" and other recent Rays.†

The Permian specimens of Pleuracanthus (Xenacanthus) found in Germany elucidate many important details in the anatomy of the interesting Selachians whose fragmentary remains have just been noticed. Some examples, in fact, exhibit nearly all the hard parts of the fish in their proper relative positions. The body is slightly flattened, and the general shape recalls that of Rhina; there are numerous teeth, of the Diplodus type, in the jaws, and the large

* Quart. Journ. Geol. Soc. London, vol. xxxvi. (1880), pp. 331-336. References to previous literature are here given. +Ann. and Mag. Nat. Hist." [4] vol. i., 1868, p. 371.

We may here note that this type of tooth is not exclusively confined to Pleuracanthus, having been found in association with at least one other spine in the Lower Carboniferous, (T. Stock, " Nature," vol. xxvii. 1882, p. 22). Further, recent numbers of the American Scientific Journals contain notices of a new Shark, named Chlamydoselachus from the Japanese seas, of which the dentition is exceedingly similar; in fact, Professor Cope has ventured to refer the latter to the Paleozoic genus, but the figures show the fish to be very different in form and indicate the absence of a spine.

straight spine is imbedded in the muscular tissues at the back of the head. The structure of the paired fins, so far as can be ascertained, is singular, and there is a long dorsal fin behind the spine, but the caudal is imperfectly known. The skin appears to have been almost destitute of shagreen, and hence traces of the internal skeleton are well shown; there is evidence of the notochord being persistent, but neural and hæmal arches, with interspinous elements for the support of the dorsal fin, are distinctly visible.

known by Sir Richard Owen in his "Odontography," in 1840. The crown of the tooth is somewhat petalshaped-a peculiarity suggesting its name—and is fixed upon a remarkably long root; the cutting edge is slightly denticulated, and a number of transverse folds of enamel usually appear at the base. It is essentially a laniary tooth, and no part can have been used for grinding or crushing; but the mode of arrangement of the dentition in the mouth, and the number of its components, can only be inferred from what is known of allied forms, no very perfect

Like the group just considered, the Petalodonts constitute an extinct family, ranging only through a limited space of geological time; numerous genera, or so-called genera, are known to occur in strata of Lower Carboniferous to Upper Permian age, but none appear to have been discovered in deposits of later date. These fishes were evidently destitute of spines, and so are represented as fossils merely by teeth, shagreen, and occasional fragments of cartilage; but we are fortunate in possessing important information regarding the arrangement of the dentition in at least two of the forms, and these particulars afford valuable aid towards determining the natural affinities of the group.

The type-genus is Petaledus (fig. 111), first made

Fig. 111.-Tooth of Petalodus acuminatus.

examples of jaws of Petalodus itself having hitherto been met with. It occurs abundantly in the Lower Carboniferous, and specimens have even been recorded from the Coal Measures, but, as will presently be shown, the identification of the latter must be regarded as doubtful.

(To be continued.)

ON June 9th a statue of Mr. Darwin, executed by Mr. Boehm, R.A., was unveiled in the British Museum of Natural History, South Kensington, in presence of the Prince of Wales and a large assembly. Professor Huxley, as Chairman of the Memorial Committee, made over the statue to the Prince of Wales, who represented the Trustees of the British Museum.