HARD WICKE'S S CIENCE- G OS SIP. 



155 



dissepiment and one between, but only occasionally. 

 The dissepiments arc thin and sub-opposite. The 

 fenestrules are nearly square, and the margins are 

 slightly indented by the cells. The cells are in alter- 

 nating rows on the margins of the fenestrules, one 

 placed in each angle formed by the junction of the 

 interstices and dissepiments, and one between ; some- 

 times the cells of the angle are on the dissepiments. 

 A cell not larger than ordinary cells is placed on the 

 keel, as well as in the angle of bifurcation. In this 

 description I have adopted all that I could adopt 

 from Mr. Robert Etheridge's description from one 

 of the Appendices of the "Geo. Survey, Scotland" 

 (Sheet 23). 



Nearly all the species figured and described by 

 Phillips, in his " Geology of Yorkshire," under the 

 generic term Refepora, are now considered to be true 

 Fenestella. In F. membra nacea^ the interstices are 

 straight, equidistant, with elongated fenestrules, and 

 pores a little oblong, with tln'ck dissepiments. In 

 F. flabellata the dissepiments are thin, and the pores 

 small but prominent. In F. temdfila the dissepi- 

 ments and interstices are thin, the fenestrules rectan- 

 gular with small pores with prominent edges. In 

 F. undulata the interstices are also thin, fenestniles 

 large and irregular, with large prominent pores. The 

 species figured from Nicholson's f sketch is nearly al- 

 lied to F. laxa, which Phillips describes, from the Car- 

 boniferous and Devonian rocks of Great Britain — a 

 proof of the wide geographical range of allied species. 

 The differences in the fenestrules of F. laxa are, 

 however, from two to four times larger than those of 

 F. magnifica. In the species termed F. nodtilosa the 

 branching is very peculiar ; the fenestrules are com- 

 paratively close together, and the pores — generally 

 three in number — undulate the margin, with small 

 pores in the interstices. The interstices of F. poly- 

 porata are thick, the fenestrules large and irregular, 

 with numerous small rounded pores. In the Geo- 

 logical Survey of Scotland, several new species are 

 described in the explanatory memoir of sheet 23, but 

 the specimens discovered and described are in a veiy 

 fragmentary condition. Two of these — F. bicelhtlata, 

 already described, and F. tubercitlo-carinata — may, 

 says the author, with the discovery of better material, 

 probably rank as distinct species ; the fragments are, 

 however, well marked, and distinct from others. In 

 his catalogue of carboniferous fossils, ]M'"Coy figures 

 ten more species, as found in the British carboniferous 

 rocks. Tliey are F. carinata, crassa, ejuncida, hemi- 

 spherica, JMorrisii, mnltiporata, ocnlata, plcbcia, quad- 

 radecitnalis, and variocosa. In the Carboniferous 

 Limestone formation of Nova Scotia, Fenestella 

 plebeia (M<^Coy) was recognized by Mr. J. Kirkby as 

 common to the Permian and Carboniferous formations 

 of England. Amongst a series of Indian carboniferous 



* Fig. 89, SciENCE-Gossir, May. 



t Science-Gossip, May, p. 109. Figs. loi and 102. F. 

 jHiignifica, Nicholson. 



fossils discovered by Dr. A. Fleming, of Edinburgh, 

 and described by Professor de Koninck,* there were 

 three Polyzoa provisionally classed with Fenestella 

 and Retepora. The first of these, F. megastoma (De 

 Kon), has a faint resemblance to F. crassa of M'"Coy. 

 " It is composed of rays which are sub-parallel with 

 each other, and the visible surface is garnished with 

 very small longitudinal stride, similar to those which 

 ornament one of the surfaces of some other species." 

 The non-poriferous side only of this species is known ; 

 and, judging from this, the species differs from F. 

 crassa by the much more shortened shape of its 

 fenestrules and the distance of its principal branches. 

 There is another Fenestella among the Indian fossils 

 which De Koninck names F. Sykesii, the figure of 

 which has some resemblance to an Irish specimen in 

 my own cabinet. The Indian " Polyzoa is fan- 

 shaped, irregularly plaited, composed of a number 

 of rays soldered one to the other, the direction of 

 which is indicated solely by the feeble thickening, 

 and especially by the series of small circular openings 

 which border them. The arrangement of the open- 

 ings demonstrates sufficiently that the rays bifurcated 

 once, or several times, during the development of 

 the polyzoarium, and that this bifurcation is the 

 principal cause of its rapid enlargement. The 

 openings are almost all the same size, and are little 

 more than half a millimetre in diameter. One may 

 generally count seven in the breadth of a centimetre. 

 There is no trace of pores and strise on the surface of 

 the specimen, although it is perfectly well preserved."+ 

 The same description will suit the Irish species from 

 Athlone, with this exception : the polyzoary is much 

 more delicate than the Indian species, and the 

 openings (fenestrules?) count about twelve to the 

 one-eighth of an inch, both ways, and the shape of 

 the openings is hexagonal instead of circular. 



One remarkable genus of recent Polyzoa approaches 

 the Fenestella, not so much by the development of the 

 cell as by the fenestrate appearance of the poly- 

 zoarium. The genus was established by Kirchenpaur, 

 and called Retihornera. " The zoarium is foliaceous, 

 composed of sub-parallel branches connected by 

 transverse tubules, so as to form an expanded frond 

 with quadrangular fenestr?e. " M'^Gillivray's species, 

 discovered among the Australian Polyzoa, is placed 

 by Busk among this genus, with the remark that 

 " Herr Kirchenpaur's genus Retihornera would, 

 from his descriptions, appear to include some Es- 

 charidan or cheilostomatous forms approaching Rete- 

 pora ; but amongst them, his R. dentata and plicata 

 appear without doubt to be cyclostomatous ; and I 

 have therefore ventured to appropriate his expressive 

 appellation for the fenesti'ate forms of hornera, not 

 regarding it, however, as impossible that the fossil 

 genus Fenestella may have a prior claim after all."+ 



* Quarterly Journal 0/ Geo. Soc, vol. xix., 1862. 



t De Koninck, ibid. 



% Busk's "Mus. Catalogue," Part III., page 20. 



