DESCRIPTION OF CHALK CORALS. 303 
blance to detached fragments of the English cretaceous zoophyte. That body 
however is considered by M. Milne-Edwards! to have no analogy with Retepore ; 
and the fossil under consideration belonging to the family Tubuliporide cannot 
also be assigned to that genus. 
It consists, as shown in figs. 3,4 &5, Tab. XVIII. B., of numerous main branches 
diverging from a centre, and giving off many lateral shoots of variable extension. 
The exterior presents on one side (fig. 3a) two sets of pores, one large and con- 
stituting the visceral cavities, the other smaller, but differing from the former 
structurally only as respects dimensions: the opposite or reverse side (fig. 4a) is 
altogether destitute of pores, and exhibits more or less distinctly longitudinal 
translucent lines with opake intervals, the representatives of tubes ; also irre- 
gular longitudinal ridges, and curved furrows in the points of partition of the 
branches. The interior of the coral was greatly obscured in some cases by mi- 
neralization ; but in the best exhibited transverse sections, large and small tubes 
or pores were intermingled, occupying the whole area, and they had a consider- 
able downward range at a variable angle (figs. 4b, 4c). 
In the tubular cavities opening on only one side, a resemblance with Hornera 
exists’, but there is otherwise no outer agreement, that genus not being provided 
with a secondary series of pores on the front surface, the characters of the re- 
verse side being also different, as well as the general mode of thickening the 
coral. The occurrence of primary apertures on but one side, and the form of 
the protruded portion of the cavities, present agreements with the Pherusa of 
Lamouroux®; but if the description of that genus be rightly understood, ‘ the 
cells” differ in their characters, being stated to be tubular in the projecting part, 
large and compressed below‘, whereas in the chalk fossil they are tubular through- 
out. Whether such a deviation exist or not, Pherusa has no series of secondary 
pores, and necessarily wants the important peculiarities which are noticed in the 
following paragraph. As respects Heteropora® and Siphoniodictyum’, it may be 
sufficient in this place to remark, that in the former genus the primary tubes are 
* Lamarck, edit. 1836, t. ii. p. 284, Ret.? ramosa. 
> Consult M. M.-Edwards, Mém. sur les Crisies, &c., art. Hornera, Ann. Sc. Nat. 2nde série, Zool. 
t. ix., or Recherches sur les Polypes. 
* Exposition Méthodique, p. 3. tab. 64. figs. 12-14; also Hist. Polyp. corallig. flexibles. 
* Hist. Pol. coral. flexibles, English Trans. p. 52. 
° Man. d’Actinol. p. 417. 
° Journ. Geol. Soc. Lond. vol. v. pp. 90, 94 et seq. 
