270 THE MEDALS OF CREATION. Cuap. VII. 
(Phil. York.), and in the Silurian deposits (Sil. Syst.). It 
may be useful to state, that in the description of the fossil 
retepores, the openings in the net-work are called fenestrules 
—the spaces between the ends, dissepiments—and those be- 
tween the fenestrules, enterstices. A delicate fossil retepore 
from the mountain limestone of Yorkshire (R. flexa), is 
figured Lign. 89, fig. 13. 
FENESTRELLA.—Cells very small, indistinct externally, with 
small prominent openings; polyparium stony, fixed at the 
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base, composed of branches, which inosculate by growth, and — 
form a cup. Numerous delicate corals, formerly arranged 
as Netepore, occur in the Silurian rocks, and have been 
placed in this genus by Mr. Lonsdale. (Sil. Syst. p. 677.) 
PETALZPORA* PULCHELLA. Lign. 69, fig. 1.—This beautiful 
cretaceous coral is “tubular, free except at the base ; frame- 
work composed of vertical laminz, with an intermediate 
foraminated structure ; apertures to the tubular cavities dis- _ 
tributed over the surface; exterior varying with age.” It 
has slender round dichotomous branches, and the polyparium 
when entire must have formed an elegant plexus of coral. 
A layer an inch thick, full of branches of this zoophyte, is 
exposed on the face of the chalk cliffs, near Dover; and 
beautiful masses, several inches square, made up of this 
coral, Idmonea and Pustulopora, may be obtained. The 
microscopic specimen figured in Lign. 69, was obtained with 
many other corals by washing chalk with a brush, and ex- 
amining the detritus deposited. 
Pustutopora. Lign. 89, fig. 8.— Another very common 
tubular branched coral of the Dover chalk; the tubes are 
cylindrical, their apertures are arranged in annular or spiral 
rows, and slightly projecting, giving a pustulous appearance 
to the stem and branches. Specimens covering a piece of 
chalk six or eight inches wide, and a foot long, have been 
discovered. The example figured is a very minute branch. 
* Mr. Lonsdale, Dixon’s Fossils, p. 285. 
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