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YOUNG—CELL-PORES, ETC., OF POLYZOA. 211

XXVIII.—NOTES on the PERFECT CONDITION of the CELL-PORES and other POINTS of STRUCTURE in CERTAIN SPECIES of CARBONIFEROUS POLYZOA from WESTERN SCOTLAND. By JOHN YOUNG, F.G.S. [Read 9th October, 1879.]

DURING recent years the beautiful and interesting group of organisms forming the Polyzoa, or , as they are often termed, found in the Carboniferous limestone strata of Scotland, have received a little attention, and the result has been the recog­ nition of a number of new forms and new characters in formerly- described forms. This has led to the provisional establishment of several new genera and species described by Mr. B. Etheridge, jun., F.G.S., Dr. Young, and myself, in the Transactions of various societies and in scientific journals of this country. These forms have chiefly been obtained from the Carboniferous limestone shales of Western Scotland, in which Polyzoa are abundant and generally well preserved. Having formed a pretty large collection of these organisms, now numbering some 40 good species and em­ bracing 16 genera, I am now able to offer a few remarks on what I believe to be the perfect condition of the cell-pores and other points of structure in several of the species, which may, perhaps, enable future investigators to place them in their proper zoological posi­ tion among the Polyzoa. I think that much importance will yet come to be attached to the perfect condition of the cell-pores and other points of structure, and that any new discoveries in this line of research will in the future be considered of much more importance than the mere finding of new genera or species. In the Quarterly Journal of the Geological Society for 1874, Dr. Young and I called tbe attention of palaeontologists to what we consider the perfect form of cell-pores in one form of the genera and Glauconome, in which the cells are closed by eight slender converging rays or denticles, and in which a very small secondary pore or pit is seen to be placed close to and in line with every rayed cell. Previous to our discovery no similar structure of cells had ever been described in either of these two genera, and as we believed these new and peculiar characters were sufficient to enable us to establish new generic and specific distinctions for these forms, we named the first Actinostoma Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

212 TRANSACTIONS OF THE GEOLOGICAL SOC. OF GLASGOW. fenestratum, and the second Glauconome stellipora. Since that time I have found, I believe, the rayed cells in another of the Fenestella, which approaches F. tenuifila, Phillips, in character. In this last form, however, the rayed cells have not been so well preserved, Jbut I still hope that better specimens will turn up to prove the point. These rays or denticles seem to have been very easily abraded and destroyed, and in most cases this is seen to have been done before the fronds of the Polyzoa were entombed in the sediments in which they now lie. When this is the case the cell mouths have a rather ragged appearance when partially worn, and when fully worn they are round openings, as in the cell-pores of ordinary Fenestella. Fronds of Actinostoma in my collection show in the same specimen every condition, from the perfect rayed pore to the round open cell. It is, therefore, only the most per­ fectly-preserved specimens which show the peculiar characters upon which the genus is founded. In the Geological Magazine for June, 1877, Dr. Young and I called attention, in a short note, to another form of cell-pore which I had discovered in certain Carboniferous Polyzoa, and which I am now inclined to believe is the perfect cell-pore of these forms. In it the mouths of the cell-pores are covered by a thin calcareous disc or diaphragm pierced in the centre by a very minute pore just visible with an ordinary pocket lens, but well seen under a low power of the microscope. At first we had some doubt as to whether this calcareous layer was not due to subsequent incrusta­ tion over the face of the Polyzoa on which it occurs, the cells being kept open through the small pores by the organism itself or by other agencies. Now, however, I have found it in the following species—Fenestella plebeia, M'Coy; F. ejuncida, M'Coy; Folypora tuberculata, Prout; and Glauconome elegans, Young and Young; and in specimens from different horizons of strata. I therefore believe that it is only another condition of the perfect cell-pore in these forms of Polyzoa, and if this view should prove correct it will perhaps necessitate the separation of the forms possessing this character from the genera amongst which they are at present located. The localities from which I have obtained Polyzoa show­ ing this character are the limes ton o shales of Hairmyres, East Kilbride; and Newfield and Dykehead, High Blantyre. The same remarks, which, as I have already stated in speaking of the Actinostoma, apply equally to the preservation of the cells in these Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

YOUNG—CELL-PORES, ETC., OP CARBONIFEROUS POLYZOA. 213 forms only the most perfectly preserved fronds show the thin diaphragm covering the cells, while, if the specimens are the least worn, the cells are seen to be round and open. In Diastopora (Bernicea) megastoma (M'Coy) we have an encrusting Polyzoon which is very abundant in the limestone shales of the West of Scotland. This species is described by M'Coy as having the cells very large, prominent, and of a semi-circular form, and having a raised edge omy to the superior half of the margin. Our specimens show that the cells were of a trilobed form, hav­ ing two small tooth-like projections on the upper lip of the cell; but, in addition, I have been fortunate in finding in the shales of Capelrig, East Kilbride, examples of this species, showing besides that the perfect cells were closed by a thin calcareous cover, pierced by a narrow transverse slit or opening just under the raised lip of the cell j and, further, that amongst the cells there is a minute cellular structure, best seen on slightly worn specimens. None of these characters are noticed in the description of the species by M'Coy, and I therefore bring them before the Society for the first time, as an additional contribution to the perfect cell structure of this species. From the shales of Capelrig I have also another incrusting organism attached to a crinoid stem, which so much resembles the incrusting form of the coral Stenopora tumida—if that is really a coral—that I have hitherto been inclined to identify this specimen with that species. I now, however, begin to have some doubts on the subject, from the fact that in this specimen the hexagonal cells are closed by a neat, thin, calcareous cover, pierced by a small pore or opening placed in one of the angles of the cells, and which in the numerous cells is quite regular in its position. I am not aware that S. tumida or any allied coral has ever been described as having the cells closed by a perforated calcareous disc. In this respect it more resembles the Polyzoa I have noticed in this paper, but I know of no incrusting Polyzoa with hexagonal cells having been described from British Carboniferous strata. The specimen here noticed is in a beautiful state of preservation, and I bring it before the Society in the hope that more light may yet be thrown upon it. Having gained a knowledge of the fact that certain of the Car­ boniferous Polyzoa have their cells closed in, either by rayed denticles or calcareous diaphragms, may we not, therefore, reason­ ably conclude that in many of the other forms belonging to the Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

214 TRANSACTIONS OF THE GEOLOGICAL SOC. OF GLASGOW. same or closely allied genera they had also similarly constructed cells, but that, owing to the state of preservation in which the latter have been found, these new characters have not as yet been noticed ? It is, however, probable that when better preserved specimens turn up some of these characters will yet be discovered. It is therefore very desirable that every specimen which falls into the hands of collectors should be carefully examined under the microscope. Of the 40 species which I have found in our limestone strata the genera of Fenestella and Glauconome are most numerously repre­ sented. In a recent paper by Mr. G. W. Shrubsole in the Quarterly Journal of the Geological Society, for May, 1879, he reviews the species of the British Carboniferous Fenestellidae. He states that of the 26 described species, he finds he can reduce them to five. While, however, I quite agree with Mr. Shrubsole that a number of the species have been founded upon imperfectly pre­ served fragments, in which some of the external characters were probably obscured, and which must now be regarded as synonyms of the species he admits, yet he seems to have failed in recognising some important distinctions which mark at least one or two of the Scottish forms. I here refer to his confounding Fenestella plebeia (M'Coy) with F. tuberculocarinata (Etheridge, jun.). These are the two most abundant Scottish forms, and as found in our beds are quite distinct under every aspect; the former having four pores on the average to each side of the length of the fenestrule, while the latter has only three. I have found these characters are con­ stant in a large series of specimens. After a careful examination of my specimens I find that we have at least eight good species of the genus, exclusive of Actinostoma, now a sub-genus of the Fenestellidse. The external characters upon which I rely are chiefly the number of pores in the length of the fenestrule, their size and form, with other surface markings; and now by the asphalte process which I have adopted, whereby large fronds can be mounted with their celluliferous face upwards, the constant character as to the number of pores can easily be traced over comparatively large surfaces of the polyzoarium. Before passing away from the Fenestellidse, I may mention another character which I have discovered, while preparing trans­ parent sections for the microscope, the significance of which in relation to the organism is not yet fully understood. When por­ tions of the fronds of Fenestella are ground down so as to show Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

YOUNG—CELL-POKES, ETC., OF CARBONIFEROUS POLYZOA. 215 the middle of the cells, a small tooth-like projection is then seen, placed on the outer wall of the cell on each side of the interstice. This is beautifully seen on one specimen of Fenestella multiporata, and also on F. plebeia, and is probably characteristic of other species of the genus. It was also independently discovered by Mr. A. W. Waters, and was figuredan d described by him in the Transactions of the Manchester Geological Society for 1878, from specimens sent him from Hairmyres, East Kilbride. In his figure and description two denticles or teeth are shown in each cell, one on each side, whereas all my specimens show only one tooth, which, as, previously stated, is placed on the outer wall and projects obliquely upwards into the cell. If there is no mistake in the understanding of Mr. Waters' section of the polyzoon, it may probably be a different species from those which I have examined.* In the Quarterly Journal of the Geological Society for 1874, Dr. Young and I discussed the affinities of the organic processes found projecting from the fronds of the fenestrated species of the Polyzoa, termed Falceocoryne by Prof. Duncan and Mr. Jenkins. We showed by figures of numerous specimens that they had no hydrozoal affinities, as we considered that they were merely pro­ cesses developed from the fronds of the polyzoon, to which they were seen to be organically attached, not incrusting or parasitically attached, nor closing up numerous cell-pores as stated by Duncan and Jenkins, as several well-preserved specimens testify. Our views were not accepted by the above-named gentlemen, but I am glad to see that one or two observers of the fenestrated Polyzoa since that date agree with us that these processes are part and parcel of the organisms. Further information on the Falceocoryne and on the development of the Fenestellidse may be found in an interesting paper in Science Gossip for October, 1879, by Mr. G. R. Yine of Sheffield. * Since the above was written, I have discovered that the small tooth­ like projections are due to a sudden infolding of one edge of the outer cell wall at that point where the cells bend from their nearly vertical position within the interstices, so as to allow their circular orifices or mouths to open on the face of the frond at almost right angles to that of the lower portion of the cells. This feature is well seen in one or two recent sections which I have made, as well as in etched specimens of the celluliferous surface of fronds. These show clearly that the infolding only takes place on the outer edge of the cell, and that consequently there is only one tooth-like projection in each cell, it being the infolded portion of the cell wall. Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

216 TRANSACTIONS OF THE GEOLOGICAL SOC. OF GLASGOW.

The genus Glauconome, as found in our beds, is represented by some eight or nine apparently good species, which are easily dis­ tinguishable from one another by various external characters. They have been exaniined by Dr. Young and myself, and as we failed in getting any descriptions or figures of the genus found in other Carboniferous strata which agreed with the characters of our Scottish specimens, we have been forced provisionally to describe and figure the group as new in the Proceedings of the Natural History Society of Glasgow. Whether we were right or wrong in doing so with all the species, we leave in the hands of future investigators of the group to declare. Of the other 14 genera of Carboniferous Polyzoa which are found in our limestone strata, the greater number are represented by only one species, others by two or three, all having good distinguishing external characters by which they may be easily known. For a complete list to date, see the Catalogue of Western Scottish Fossils prepared for the meeting of the British Association in 1876. In the Annals and Magazine of Natural History for 1874, Dr. Young and I called attention to a new internal point of structure in one of the Polyzoa—the Millepora gracilis of Phillips,—and I have also discovered the same character in M. rhombiferaoi the same author. In these species we showed that the cells are arranged in a spiral form around a central tubular axis or rod, a character not pre­ viously noticed in any polyzoon recent or fossil. For these forms we established the genus Rhabdomeson, the two species of Phillips mentioned above being noted as R. gracile and R. rhombiferum. We stated in our paper that beautiful natural sections of the organisms were found in the white polyzoan band of limestone in Trearne Quarry, near Beith, showing the middle rod around which the cells are arranged in a very clear manner, when the organism happens to be split lengthways. Since that date even better pre­ served examples have turned up in the same bed. At Auchen- skeoch Quarry, Dairy, I recently found on a slab of shale a branch­ ing specimen of R. gracile which showed that the organism sometimes attained a length of six inches or more, and that its surface ornamentation was very spinulose around the margins of the cell openings when well preserved. Other researches among branching forms of Polyzoa with nearly the same habit of growth as Rhabdomeson have failed as yet in finding any middle axis, and probably in those it did not exist. I Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015

WHITE—ON ROCKS AND MINERALS IN CORNWALL. 217 still think, however, that many interesting points yet remain to be discovered in the Carboniferous Polyzoa, both as to the perfect form of cells and other points of internal structure. I say so all the more readily from a knowledge that all the facts of interest noted in this paper, whether regarding the discovery of new points of structure in the Polyzoa, or the descriptions of new species by Dr. Young, myself, and other investigators, are the result of work conducted at intervals only during the past six years. I have no doubt, therefore, that continued research will reveal many other points of interest and value regarding this till lately comparatively unworked but extensive and interesting group.

[ABSTRACT.]

XXIX.—On ROCKS and MINERALS in CORNWALL. By JAMES WHITE.

[Read 13th November, 1879.]

MR. WHITE said that the strata in Cornwall are chiefly , but are much broken up and metamorphosed by the action of igneous rocks, traps, porphyries (locally known as "Elvans"), and granites. These latter are of many varieties of hardness and texture, and are used—the harder, for ornamental and heavy building purposes,' like our own Aberdeen, Peterhead, and Mull granites; the softer and more earthy varieties, for the manufacture of china clay, of which about 80,000 tons are produced annually. London Bridge, and Waterloo Bridge, in London, and the docks at Chat­ ham, are built of Cornish granite. The chief feature of the county, however, and that which has brought Cornwall its greatest riches, is the abundance of its metallic veins. The Cornish mines have been known and worked from time immemorial, in the ordinary, though not the geological, sense of that well-worn phrase; it is known that long before the Christian era Phoenician sailors visited the coast and other parts of the county for the purpose of trading in tin and various other metals. Tin occurs nowhere else in the British islands, and is here found in two forms—stream tin and vein tin. The former is found from the size of small grains to lumps of lOlbs. to 121bs. weight, while occasionally large masses of rock occur richly impregnated with the mineral. These are found scattered over the surface of the hard