CORALS FROM THE SILURIAN FORMATION. 251 
them being, in general, equal to twice, and sometimes to thrice their diameter. The 
polygonal divisions of the coonenchyma are very regular in form and in size; their breadth 
is about half of a line. 
A vertical section of this fossil shows that the walls are very distinct, and the tabule 
closely set, and in general placed horizontally, but sometimes slightly oblique. The 
appearance of the ccenenchyma differs in the upper and lower parts of the corallum; near 
the upper surface, to the depth of about 1 line, the vertical lmes corresponding to the 
section of the prismatical lamina of the tubes, are much more strongly marked than the 
horizontal lines that correspond to the sections of the trabicula or small intratrabicular 
diaphragms ; but in the lower parts of the corallum a contrary disposition exists, and the 
transversal lines running nearly parallel to the surface of the compound mass, are the only 
ones which are distinct to the naked eye. 
H. Murchisoni is found in the upper Silurian deposits of Wenlock Edge. Professor 
M‘Coy has met with it at Aymestry, in Herefordshire; at Coniston Waterhead, in Lan- 
cashire ; and at Llansantfraid, in Denbighshire. It is found also in Gothland. 
Specimens are in the Collections of the Parisian Museum, of the Museum of Practical 
Geology of London, of M. de Verneuil, and M. Michelin. 
This fossil coral differs from ZZ. interstincta’ by the greater distance between the calices, 
and the abundance of the ccenenchyma. It much resembles 4. porosa” by its external 
characters, but differs from it by the structure of its ccenenchyma; the horizontal lamine 
of that tissue being much more developed than the vertical ones, whereas the contrary 
takes place in /Z. porosa. 
3. Hexiotires MeGAstomaA. ‘Tab. LVIII, figs. 2, 2a, 26, 2c, 2d. 
to) - ) 
PorrITES PYRIFORMIS (pars), Lonsdale, in Murchison, Silur. Syst., p. 686, pl. xvi, figs. 2d, 2e 
(ceet. excl.), 1839. 
Porites MEGASTOMA, M‘Coy, Silur. Foss. of Irel., p. 62, pl. iv, fig. 19, 1846. 
GeororitEs INTERMEDIA, D’ Orbigny, Prodr. de Pal., vol. i, p. 49, 1850. 
PaLMoPora MEGASTOMA, M‘Coy, Brit. Palzeoz. Foss., p. 16, pl. ic, fig. 4, 1851. 
Herouires mecastoma, Milne Edwards and Jules Haime, Pol. Foss. des Terr. Palzeoz. 
(Arch. du Mus., vol. v), p. 216, 1851. 
HELIOLITES MacrostTyLus, J. Hall, Paleont. of New York, vol. ii, p. 135, pl. xxxvi a, 
fig. 2, 1852. 
Corallum composite, massive, irregularly hemispherical; sometimes adherent, sometimes 
free. Epitheca of the under surface not much developed. Ca/ices having all nearly the same 
dimensions in the same specimen, but varying from two thirds of a line to 1} line in different 
specimens ; very closely set, quite circular, and with a margin not prominent, and scarcely 
1 See tab. lvii, fig. 5. 2 See tab. xlvii, fig. 1. 
