As species of Fenestella are very common as fossils in the

Devonian rocks, but especially those of Tasmania, a few observations

on the genus and its affinities will be found

useful to geologists,

Fenestella is a genus placed now by all palaeontologists in

the Class Polyzoa, Order I, Infundibulata

Tenison Woods, Julian Edmund

University of Tasmania Open Access Repository

46ON THE GENUS FENESTELLA.By the Eev. J. E. Tenison Woods, F.G.S., &c.[Bead Sth June, 1875.]As species of Fenestella are very common as fossils in theDevonian rocks, but especially those of Tasmania, a few-observations on the genus and its affinities will be founduseful to geologists,Fenestella is a genus placed now by all palaeontologists inthe Class Polyzoa, Order I, InfuncUhidata.Sub order Cheilostoniata, that is to say, with the aperture ofthe cell filled with a thin membranaceous or calcarious velum,with a crescentic mouth provided with a movable lip. Thislatter feature in the case of Fenestella is concluded fromanalogy and certain anatomical details, because the fossilsthemselves are never so perfectly preserved as to manifestthem.Fenestella is also placed in the subdivision S. inarticulataor continuous, and in the section himultiserialaria, that is,the cells disposed in a double or multiple series. It is alsoplaced by most authors in the family Escharidce, of which thedefinition is as follows :—Polyzoarium erect, rigid, foliaceous,and expanded, lobate, or reticulated. Cell disposed quincun-cially in the same plane on one or both sides ofthe polyzoarium.But in some cases this hardly applies, as the cells are some-times, as in the case of F. internata, Lonsd. in a double seriesonly. The genus was also placed with the Retepora, of whichthe definition is foliaceous, calcareous, reticulated, cells im-mersed opening on one surface only. But in 1830 Mr. Millersuggested a new genus for certain reticulated polyzoa in thecarboniferous limestone which Mr. Lonsdale adopted. Allcup-shaped reticulated polyzoa were hitherto called Eetepora,but now it was agreed to name Eeteporathose only on which theopenings of the cells were inside the cup, and those in whichthe cells opened on the outside only were henceforth erectedinto a new genus, and called Fenestella. But difficulties inapplying his distinction soon arose. The cup-shaped orconical figure is nearly always absent. In Tasmania thedistinction would be of no avail. The polyzoary, though verywavy and irregular, is always fragmentary, and often lies per-fectly flat. Prof. Phillips suggests (Pal. Foss. of Cornwall,Devon, &c., p. 22) another mark of distinction. He says thatthe non-poriferous surface of Fenestella is usually marked bylongitudinal, more or less continuous ribs, united by bars ofsmaller diameter, leaving oval or subquadrangular spaces.In Eetepora these spaces look more like holes or perforations47through the coral. The external poriferous interstices ofFenestella ai-e in several species, but perhaps not in all,carinatcd in the middle.It seems to me that there is a better mark of distinctionthan this, at least for the Tasmanian species. In Retepora theholes are at rarer intervals, and the term bars cannot beapplied to the tissue above or below them. It is a mass ofcells like the rest of the polyzoary. In Fenestella the barsare sparsely celluliferous. There are calcareous points ofattachment to give mutual strength and support to dichoto-mously dividing and spreading ligulate series of cells. Thetransverse bars are much narrower than the celluliferous por-tion, and they are given off almost at right angles, and in somespecies only very slightly arched. It is this peculiarity whichcauses the interstices to be more quadrangular than oval.Prof. Phillips thus defines the genus Qoc. cit.) :—" Greneralfigure spreading from a narrow base to an infundibuliform orfoliaceous figure ; substance, a thin stony expansion, com-posed of slender radiating or longitudinal ribs variously con-nected by transverse bars, so as to constitute a more or lessregular open network. lie adds (but the italic words markedby me do not apply to all the Tasmanian species) the longitu-dinal ribs margined on each side by one row of pores on theouter face only."It must be always borne in mind that we very seldom findanything but casts of these beautiful fossils. The calcareousmatters have been so completely dissolved away that nothingremains of the old polyzoary. The casts too seldom show anymarkings of the front or back of the cells. The most ofthe specimens preserved by collectors are valueless as showingany details. They are merely impressions of the intersticesor net-work markings, and nothing more. Those who arevery familiar with the species might determine them from thisalone, but it is hardly a safe identification. There are, how-ever, in the Museum of this Society some specimens fromMaria Island, where the whole polyzoary has been beautifullypreserved. The calcareous matter is untouched, and the detailof the cells is plainly evident. In one species, Fenestella ampla,there is a raised margin round the mouth and circular depres-sions, probably for avicularia. In one place also there is theembossed dome of what appears to be an ovicell. Thus thefunctions of nutrition and reproduction were in no way diffe-rent from the polyzoa of the present day. It is seldom thatBuch an opportunity is offered for studying the details of theseinteresting organisms. Pi-of. Phillips {loc. cit.) says " thatowing to the decomposition of the whole or part of the coral-line substance iu argillaceous rocks these beautiful fossils48must be studied in such cases by very careful comparison ofthe impressions of the surfaces. In limestone beds tlie sub-stance is often well exposed by atmospheric influences, but insuch instances the poriferous face seldom clearly appears,owinof appai-ently to tbe former adhesion of this face to therock." This passage is especially applicable to the fossils ofTasmania. In most cases we have only impressions onargillaceous rocks, while the well preserved specimen now re-ferred to is a limestone rock. Here but for the dark compactsurrounding matrix and the accompanying mass of Steno2)oraovata Lonsd. the white crystalline network of Polyzoan frag-ments might almost seem to be from the Polyzoan limestone ofthe middle Cainozoic of Australia. Butexce2:)t in few instancethe fossils are most pi'ovokingly nearly all face downwards.There are 28 known species of Penestella in British rocksaccording to Morris' Catalogue, in which are none of theAustralian species. They range from the L. Silurian to thePermian formation, but their princijjal horizon seems to bethe Devonian. Three species and a variety are known inTasmania, the species all represented in Australia and thevariety also probably. They are thus described :—Fenestella ampla Lonsdale.* Cupshaped, celluliferous, sur-face internal, branches dichotomous, broad, flat, thin ; meshesoval ; rows of cells numerous, rarely limited to two, alternate;transverse connecting processes sometimes cellular ; innerlayer of non-cellular surface very fibrous ; external layer verygranular, non-fibrous, gemmuliferous vessel small." Among the specimens of this coral," continues Mr.Lonsdale, " contained in the collection under consideration wasone which afforded some interesting changes dependent uponage, the absence of which in the series originally examinedwas alluded to in the species. In the uppermost portion ofthis specimen the casts of the cellular surface exhibitedsimilar characters to those displayed in Mr. Darwin's series^with the addition occasionally of a crescent-shaped impressionunder the mouth, and due, it is believed, to a local modifica-tion of tbe sculj^turing on the surface of the other cells. Alittle lower the ridges, or furrows representing, them began todisappear, and still lower by a further thickening of theexterior all traces of them were obliterated, the interspacesbetween the mouths displaying irregular protuberances ; andthat which was considered as a state bordering upon decrepi-tude exhibited casts of minute oral apertures, with longerprojections immediately beneath marking the original exten-• These and the two following descriptions are taken from Darwin's Geo-logical Observations in South America, etc.,page 1(53. Appendix. Quotedalso in Strzelecki's New South Wales and Van Diemen's Laud, page 2G8.49Bionoftlic uioutlis." Query,Wove tlioso protubevanoos ovicells-Fenestt'Ua intcrnata, Lonsdale. Cup-shapeJ ; celluliferoiissurface internal ; branches dichotomous compressed, breadthvariable; meshes oblong, narrow ; rows of cells, 2—5, dividedby longitudinal ridges; transverse connecting pi'ocesses short,without cells ; non-cellular surftice, inner layer sharply fibrous,outer layer minutely graiuilar.Fenes'tella Jhssula. Lonsdale. Cup-shaped; celluliferoussurface internal ; branches dichotomous, slender ; meshes oval;rows of cells two ; transverse processes non-cellular ; innerlayer of non-celluliferous surface minutely fibrous, externallayer smooth or granular.Variety a F. dcnsa. Ethcridge.* Of this variety, if it benot a distinct species, Mr. E. says:—"Form of polyzoariumnot known, probably cup-shaped, one portion is foliaceous,meshes or fenestrules oval, small, densely arranged upon theexpanded coenoecium or polypidom, transverse processes or barsnon-cellular. These unsatisfactory casts of Fenestella I referto Lonsdales species F. fossula. No good characters are leftfor determination. The transverse processes or bars and thefenestrules are so obscure that any attempt to give definitecharacters would mislead. It so closely resembles F. fossulafrom Mount Wellington, Tasmania, and St. Patrick's Plains,New South Wales, that I feel obliged to refer it to that form.Any additional species would only multiply names. I had,however, proposed the name of F. densa for this Queenslandspecimen. The original habit was probably infundibuliformor cup-shaped ; but whether the bars were rectangularlydichotomous with oval meshes, cannot be distinctly made out.Locality, Gympie, Queensland, Smithfield reef. Form,Devonian.It will be seen that the above characters differ from what Ihave said on the cup-shape which many specimens in theMuseum will show to be untenable, and in the transverse barsbearing cells. But as the observations were all apparentlymade from casts mistakes might easily arise.We may now enquire, what are the affinities of the genusFenestella, or its relations with other genei-a. It cannotstrictly speaking, be classed with Eetepora for the reasons Ihave given. As a slender ligulate polyzoarium strengthenedand held together by transverse bars its disassociation fromEetepora is very evident ; and this is plainly seen in theBritish Devonian species, F. laxa, Lons., where the bars areirregular at rare intervals, and giving rise to interstices ofthree or four lines square. Among existing polyzoa we have• Proceedings of Geological Society, April 24th, 1872, p. 332.50sucli a form in Cauda arachnoides (Lamouroux Encyclop,Methodique 5, p. 64, figs. 18 to 22), where the branches areconnected with tubular fibres, but these are flexible, horny,and not calcareous. There is, however, a species of Hornera,R. GamUerensis, Busk, in the polyzoan limestone of MountGambier, a middle cainozoic tertiary fossil, where the ligulatecelluliferous portions are united bv transverse calcareous bars.The analogy of this fossil to Fenestella is very great. InHornera, however, the back of the cells shows concentric ridgesof growth, whereas that of Fenestella is fibrous. The casts ofthe two forms are the same, and widely as they are separatedin point of time, I am much inclined to the opinion thatHornera Gamhierensis is one of the recent analogues of theDevonian Fenestellae.Were these fossils entirely calcareous ? In answer to thisit must be remembered that a corneous substance, the natureof which has not received the attention it deserves, forms theroot byssus or point of attachment of many polyzoa. It alsoforms the point of attachment between each cell in Catenicella,and the junction of the internodes, in Calpidium, Salicornaria,&c. I have reason to believe that it lines the cells inall polyzoa. Something like that is seen in Catenicellaunder the microscope. In examining many hundred specimensI remarked that similar species showed the same opticalpeculiarities under the polariscope. In Catenicellse these weregenerally slight ; in Bugula on the other hand most brilliant.(Sometimes when the whole calcareous portions of Fenestellaare removed, there remains a series of rounded cells, whichare not effected by acids. These may be the corneous liningof the cells. It would seem from the fact that a calcareousroot is never seen in Fenestella, that it had a fibrous byssuslike Cauda, &c. How these bars and extra cellular portionsare formed is not known, even in existing species. The bodycontained in the cell must not, however, be considered as anindividual. Indeed, in living species when thousands ofthe cells are open one of them is touched, the whole drawback, and close instantly. We must consider the polyzoariumlike a plant with leaves, bark, buds, flowe'rs, seeds, and thedifferent processes belonging to each. These constitute onewhole which they subserve by different functions endlesslyrepeated in one individual.Finally the fewness of species of one genus, though indi-viduals are as common as in any deposit is a remarkable fact.In recent rocks genera of polyzoa can be counted by tens, andspecies by hundreds. It must, however, be remembered thatthe past forms are as highly organised as those of the presentday, and belonging to specially developed classes.

On the genus Fenestella

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On the genus Fenestella

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