14 BRITISH PALZEOZOIC FOSSILS. [Zoopuyva. 
is the existence in the former of transverse diaphragms, as well as occasionally of distinct tubular walls to the 
cells; thus forming a passage from the Madreporacea to the Madrephyllacea by the present corals on the one 
hand, and the sixteen- or eighteen-rayed Helioporw and Pocillopore on the other. 
Genus. PALAOPORA (M°*Coy). 
Ref. and Syn.—M°Coy, Annals Nat. Hist. 2nd S. Vol. IIT. p. 129. > Geoporites (d’Orb.) Prod. p. 49, (1850.) 
> Plasmopora (Edw. and Haime.) 1849. > Propora, id. 
Gen. Char —Corallum polymorphous, generally subhemispherical and concentrically ridged beneath, rarely 
branched; formed of cylindrical, distinctly walled, tubular cells, having internally twelve vertical sulci, or 
rudimentary lamellze, and divided at irregular intervals by transverse diaphragms ; the tubes surrounded and 
connected by a uniform minute net-work of small vesicular plates. 
I have proposed this genus for most of the so-called Porites of the Paleozoic rocks. First described 
by Goldfuss as Astrwa, they were removed by Ehrenberg (Ueber Corallenthiere des rothen Meeres, &c.) 
and Lonsdale (Silurian System) to the recent genus Porites, in which they were followed—probably without 
examination—by many writers; Profs. Bronn (Lethzea, &c.), Phillips (Palzeozoic Fossils), and others, have, 
however, much more happily pointed out their resemblance to Heliopora. The distinctly walled tubular cells 
visible in both sections, connected by cellular tissue, with their twelve rudimentary lamellae, distinguish the 
present ancient corals from the modern genera just named; for Porites has a minutely reticulated or lacunose 
corallum impressed by shallow, polygonal, undefined cells on the upper surface, and presenting in the horizontal 
and vertical sections an uninterrupted, irregular, uniformly vesicular structure. Heliopora agrees perfectly in 
external appearance, and in the two sections exhibits the same characters of vesicular structure, connecting 
tubular cells with transverse diaphragms, but in it the tubes have eighteen or more rudimentary lamelle, 
while they are constantly twelve in the present genus, which I only know as yet in the older and middle 
Palzeozoic rocks. The species are extremely difficult to define and discriminate, owing to the diameter and 
distance between the main tubes varying in one mass. Since the above remarks were written, this genus 
has been divided into three others by MM. Edwards and Haime; but as I am unable to appreciate the 
distinctive characters of two of them, and the third is of very obscure structure, I refer, at present, for the 
genus Plasmopora, to the description of Palawopora petalliformis; for Propora, to P. tubulata ; for Thecia, 
to P. expatiata. 
PaLtmorora? (THEctA) EXPATIATA (Lonsd. Sp.) 
Ref. and Syn.—Porites expatiata. Lonsd. Sil. Syst. t. 15. f. 3. 
Sp. Ch.—Corallum forming thin flattened, irregularly mammillated expansions ; upper surface with slightly 
impressed obscurely polygonal, close, small cells (three to four in the space of two lines), the twelve radiating 
thick, rugged lamellze of which irregularly cross the rounded intervals between the cells; no distinct inter- 
mediate tubular structure. 
This remarkable species is doubtfully placed in the present genus, from the apparent absence of inter- 
mediate tubular structure between the main tubes, although in some cases I think I have noted traces of 
them in the corners or widest space between four adjacent cells. I have been unable to see more of the 
vertical section than that the main tubes were strongly walled, and had horizontal diaphragms, two spaces 
between which rather more than equalled the diameter of the tube; in both the horizontal and vertical 
sections (only obscurely seen) the space between the cell-tubes seemed nearly solid, forming polygonal walls 
with a slight vermicular porosity. MM. Edwards and Haime have proposed for this species their family 
Theeide, and its single genus Thecia, characterized by the radiating lamellae being very much developed and 
united to form an abundant compact ccenenchyme and superficial stars. I cannot make out the internal 
structure of the coral with certainty, in any of the specimens at my disposal, but I adopt Thecia provisionally 
as a subgenus. 
Position and Locality—Not common in the Wenlock limestone of Dudley, Staffordshire, forming large 
flattened masses ; Wenlock limestone at Wenlock, Shropshire. 
