In calculating the last figure, allowance has been made for the evaporation of the water contained in the coal Some authorities give the results of analyses of coal in the dried state, but such statements are of little practical value, and are apt to mislead consumers of fuel. The water in coal, although readily expelled by heat, varies very little in samples taken from the pit at different times, and, in fact, is as constant as the composition of the coal itself, which varies sensibly in different portions of the field.

XVIII.-Contributions to our Knowledge of the Rugose Corals, from the Carboniferous Limestone of Scotland. By JAMES THOMSON, F.G.S., Corresponding Member of the Royal Society of Sciences of Liège, and Honorary Member of the Royal Ducal Society of Jena.

[Read before the Society, April 14th, 1880.]

THE following paper contains a description of several genera and species of corals from the carboniferous rocks of Scotland. Some of them have been known to me since the year 1866, and although long since satisfied that they were new and undescribed groups, I have delayed introducing them into our palæontological lists until I had accumulated a large series of specimens; and, before finally deciding either genera or species, had submitted them to some of our ablest palæontologists, both British and Foreign, and more especially to my friend, Mr. Robert Etheridge, Senr., F.R.S., &c., President of the Geological Society of London,* who kindly examined them, along with a considerable number of other genera and species, some of which have already been recorded in the Proceedings of the Philosophical Society of Glasgow, and others of which are yet to be considered. My own conclusions being in this way confirmed, I now submit them to the scientific public.

The specimen which is delineated in Plate II, Figs. 1, 1A, 1B, and 1c, is seven inches long. Fig. 1 represents the calice, which is imperfect; Fig. 1a is a transverse section taken an inch and a half below the superior extremity of the corallum; Fig. 1в is a longitudinal section three inches from the crown of the

* To whom I beg to offer my cordial thanks for thus kindly giving me the benefit of his large experience, and so aiding me in the classification of this group.

corallum; and Fig. 1c represents a transverse section one inch from the inferior extremity of the corallum. This I felt the desirability of doing in order to show that the structural characters are continuous from the superior to the inferior extremities of the corallum.

From the subjoined generic diagnosis it will be seen that I describe here for the first time a system of transverse plates that are found in the interlamellar portion of each septum (Fig. 1a), which plates, in a longitudinal section, are seen passing inwards and downwards along the inner faces of the lamellæ that form the lateral walls of the bilamellar portion of the septa (Fig. 1c)—a discovery which I made recently in microscopic sections which I prepared for the investigation of another important physiological point in the structure of rugose corals, and regarding which I hope to be able to give details by-and-by. Reference is also made to the bilamellar structure of the septa, lamellæ, and interseptal dissepiments. These I also discovered during the above microscopical investigation.

Generic Characters.- Corallum simple, cylindrical and conical near the inferior extremity, and cornute. They are tall in the cylindrical forms, while in the others they are variable; epitheca thin, with minute crenulate encircling lines, and irregular annulations of growth; calice circular and moderately deep, and in some forms everted, exhibiting in the centre of its floor a slightly elevated boss, which is formed by a series of ridges of variable number, and which are the free ends of the lamella of the central area converging inwards and upwards from the inner margins of the primary septa to the centre of the calice. The septa are variable in number and stoutness, and are of two orders. The primary never extend further inwards than to the base or outer margin of the elevated boss in the central area, and exhibit lamina for about three-fourths of their length from their inner margins, while towards the periphery they are single, thin, and more or less flexuous. The interlamellar area is occupied by minute transverse granular plates, in number from four to twenty-two in the space of a line, which in a longitudinal section are seen to pass inwards and downwards along the inner face of the lamina (Fig. 1c). The secondary septa are minute and hardly recognisable in the

vesicular tissue that surrounds the outer zone; they are united by interseptal dissepiments, which are few in number near the inner margins of the primary septa, and more or less numerous in the external area, where they form a dense vesicular tissue. The walls of the septa, the lamellæ, and the interseptal tissue consist of two layers-the inner, dense and granular; the outer, also granular, but much less dense. The fossula is variable in size in the different varieties, but usually well marked.

The longitudinal section (Fig. 2B) is triareal. The middle of the central area is composed of thin discontinuous columellarian lines, and each of these lines is united by concave tabulæ, while at the outer margin of the central area they are convex, the convexity pointing upwards and outwards. The intermediate ("interlocular") area is composed of convex tabulæ, convexity upwards, these tabulæ uniting the inner ends of the primary septa.

The outer ("interseptal") area is occupied by more or less irregular lenticular convex cells, convexity pointing upwards and inwards, and arranged in oblique rows.

The group which forms the subject of the present communication has had my attention since 1866. In the autumn of that year, I discovered in Thirdpart, near Beith, Ayrshire (Pl. I., Figs. 2, 2A, 2B), the first form, which struck me as being different from any of the genera or species that had previously come under my observation, and which certainly is not recorded in the valuable memoir of M. Edwards and J. Haime, published in the Transactions of the Paleontological Society in 1850. Since then I have frequently visited that and other localities, and I have accumulated a sufficient data to warrant me in creating a new genus for their reception. I have in my own cabinet upwards of forty well-marked varieties; meanwhile it is only those forms that are most strikingly pronounced which I have selected for specific distinction.

In the general features of the external aspect the forms which I have grouped under the name of Centrephyllum present a close resemblance to those which properly belong to Clisiophyllum (Pl. I., Fig. 6), but they are nevertheless separated by characters sufficiently distinct to warrant their being placed in a group by themselves. The generic characters of Centrephyllum agree with those of Clisiophyllum in the triareal arrangement of their structure, as shown in longitudinal sections.

In both genera the outer area consists of convex vesicles