By Recent Years the Beautiful and Interesting Group of Organisms

Downloaded from http://trngl.lyellcollection.org/ at Indiana University Libraries on July 9, 2015 YOUNG—CELL-PORES, ETC., OF CARBONIFEROUS 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 Bryozoa, 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 Fenestella 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.

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