627 
APPENDIX A. (LONSDALE ON CORALS.) 
(part ii. p. 677. 1839). Various polypidoms, however, similar in structure with the carboniferous lime- 
stone fossils to which the name was applied by Mr. Miller, having been recently referred to Gorgonk 
and Retcpora, and the establishment of Fenestella objected to', it has been deemed necessary to point 
out briefly the characters by which the latter genus is distinguished from the two former. 
From Gorgoma, whether limited according to Lamouroux, De Blainville and Ehrenberg, or considered 
more generally, as by Lamarck, Fenestella differs in its principal component structures. It has no con- 
tractile, separable, pulverulent crust, to which the cell of the polype is limited, nor has it any represen- 
tative of an internal, horn-like axis, with or without a distinct central structure. The outer lamina, 
which in a state of decomposition may be said to resemble, to a certain extent, the crust of Gorgonk', 
consists, however, m a nearly perfect condition, of an apparently solid substance, more or less pierced by 
microscopic foramina, but bearing no trace of having been contractile, or largely composed of animal 
matter. On the side to which the cells are confined, it is very thin, except at the intervals where the 
cells bend suddenly outwards ; while on the reverse side, it was not developed till the coral had attained 
a certain age, after which it was gradually thickened, and it often attained considerable dimensions in 
the lower part of the stem. In some old specimens, when this reverse lamina is partially abraded, and 
the internal layer of vertical tubuli is exposed, the resemblance to ordinary, recent Gorgonk is con- 
siderable ; but a due examination of all the component parts will convince the observer that there is no 
generic identity. In the next place, as respects the cells, the differences are as great. In Gorgonk the 
whole contractile crust, including the sides of the polype-cavities, is but a great development of the 
outer tunic of the compound animal-; whereas in Fenestellae, the laminae composing the outer surface 
and the other walls of the cells, agree closely in characters with the equivalent portions of true calca- 
reous cellular corals, and therefore had no intimate union or interblending with the membranes of the 
polype similar to that of Gorgonk. A careful consideration of these structures alone, will, it is believed 
satisfy the palaeontologist, that there is not merely a generic, but a much greater distinction. With 
regard to the interior of the coral, a perfect dissimilarity again prevails. Beneath the thick series of 
obliquely overlying cylindrical cells, limited to one side of the coral, there is no axis formed of concen- 
tric bands variously composed, yet distinct in character from the crust, but a parallel layer of vertical, 
capillary tubes, the walls of which differ not apparently from those of the cells. In the young states, 
this layer constitutes the outer surface of the non-cellular side,— a character not to be detected among 
Gorgonk, which develope, first, the perfectly surrounding crust, and then the fibrous or horn-like axis” 
1 he outer layer of the reverse side differs not, as before stated, essentially from the other solid portions, 
and was clearly formed by secretions from vessels connected with the polype by means of foramina or 
tubuli, in the same manner as in many cellular or tubular corals ; and it cannot be regarded, like the 
crust in Gorgonk, as the product of an investing animal substance. 
The characters thus imperfectly suggested for consideration, will, it is hoped, when better elucidated 
by accomplished paleontologists, lead to a right understanding of the corals assigned to Mr. Miller’s 
genus, and remove every doubt respecting their not being “ corticiferous polypidoms.” Had that author 
lived and published the intended work, the nature of these fossils would not have been misunderstood by 
any observer. 
Between Fenestella and Retepora the agreement is much greater than in the preceding case. In both 
genera the polype cells are limited to one side, and the reverse surface is formed as well as thickened by 
1 Description Anim. Foss. Terr. Houiller, &c. de la Belgique, p. 3, 1842. 
2 See Dr. Milne Edwards’ remarks on “ Polypiers Corticiferes," 2nd edit. Lamarck, Anim. sans Vert. ii. u 464 
et seq, 1836. ’ ■ ' i 
