THE CARBONIFEROUS "FENEST BLLIDJE. 



states that the perfect condition of Fenestella will be found in his 

 genus Hemitnjpa. This latter I have shown* to be a mistake due 

 to an incrusting organism on Fenestella membranacea, Phil. 



In his second definition, in 1854 -f-, which was intended to include 

 both Carboniferous and Silurian species, M'Coy is more successful ; 

 no mention is made of the particular face on which the cells are- 

 placed. He does not adequately describe the shape of the polyzoary, 

 and adopts one of Lonsdale's errors respecting a layer of vertical 

 capillary tubes on the reverse face. 



The last definition we have was by Prof. King J in 1848, after 

 arranging the Permian Polyzoa. He ignores M.'Coy's work in 

 1844, and says that the genus, as constructed by Lonsdale in 1845, 

 requires subdividing. As no trace of the incrusting coral was found 

 in the Permian species, all reference to Lonsdale's supposed mature 

 condition of the Fenestella is omitted. Prof. King's short and other- 

 wise exact account is inexact in stating that the cells are distributed 

 in two or more linear series. The true Fenestellaz have never 

 more than two rows of cells on the interstice ; the supposed row on 

 the keel does not really consist of cell T pores, but of the bases of hollow 

 spiny processes, which oftentimes, in the case of the Permian Fene- 

 stella, have been unduly distorted by a subsequent deposition of 

 carbonate of lime. 



Prom the foregoing it is evident that none of the original descri- 

 bers of the genus Fenestella has grasped the main features of it as 

 a whole. What is wanted is a definition which shall embrace the 

 whole of the Palaeozoic Fenestella;. 



The following definition is therefore proposed, after a careful study 

 of the several species ranging from Silurian to Carboniferous times. 



Genus Fenestella, Lonsdale. 



Polyzoary a calcareous reticulate expansion, either flat, conical, 

 or cup-shaped, formed of slender bifurcating branches (interstices), 

 poriferous on one face, connected by non-poriferous bars (dissepi- 

 ments) forming an open network. Cells immersed in the interstices, 

 and arranged in two longitudinal rows divided by a central keel, on 

 which are often prominences. Cell-mouth small, circular, and 

 prominent when preserved. 



Fenestella plebeia, M'Cov, Syn. Carb. Foss. Ireland, p. 29,. 

 fig. 3. 



Fenestella antiqua, Lonsd., M'Coy, Syn. Carb. Foss. Ireland, 

 p. 200. 



carinata, M'Coy, Syn. Carb. Foss. Ireland, pi. 28. fig. 12. 



devonica, Semenow et v. Moller, Bull, de l'Acad. de St. 



Petersbourg, t. vii. p. 233, pi. 3. fig. 16. 



formosa, M'Coy, Syn. Carb. Foss, Ireland, pi. 29. fig. 2. 



flustriformis, Phill. Geol. Yorkshire, pi. i. figs. 11, 12. 



fossida, Lonsd., Darwin's Obs. on Volcan. Isl. p. 166. 



* Quart. Journ. Geol. Soc. vol. xxxv. p. 282. 



t Brit. Pal. Foss. p. 49. J Permian Fossils, p. 34. 



