138 DESCRIPTION OF CORALS. 
Siderastrea Websteri. (Tab. I. fig. 5.) 
Incrusting, hemispherical, or spherical ; stars polygonal, united by a reticu- 
lated structure of variable width; lamell 24, six single and broad, with six 
intermediate groups, composed of one broad and two converging narrower plates, 
outer edge blended with the boundary reticulation, inner edge of the twelve 
broad lamelle blended with the central structure, sides sharply and thickly 
tuberculated, more or less foraminated ; centre a complex, highly perforated 
reticulation ; terminal cup shallow, nearly filled up at one period of growth; 
additional stars interpolated. 
Astrea Websteri, Bowerbank, Mag. Nat. Hist. New Series, vol. iv. p. 26, fig. 
a, b, 1840. 
This fossil agrees in general aspect with the corals to which the term Astrea 
is usually applied, but it differs essentially in its mode of developing additional 
stars from those polypidoms to which Ehrenberg has beneficially restricted the 
genus *,—that process being effected in the fossil under consideration, not by a 
subdivision within the area of the mature star, but by the production of stellular 
cavities in interspaces due to radiation. In all the leading structures, as well as 
in the developing of intermediate stars, the Bracklesham fossil agrees perfectly 
with M. de Blainville’s subgenus Siderastreat, adopting, for the sake of actual 
comparison, his second species (Ast. galawea) as its typet, both corals being com- 
posed of stars without distinct boundary-walls, and united by a reticulated struc- 
ture ; the lamelle likewise of both being similar in characters, also in the mode 
of blending with the peripheral and central portions of the star, as well as in the 
general manner of grouping. From the genus Porites, the fossil as well as the 
recent polypidom is markedly separated by the lamellz exceeding twelve, though 
there is a resemblance in the prevailing aspect of the surface. For the above 
reasons therefore, it is deemed correct to consider the Bracklesham coral as a 
species of Siderastrea ; it will however be necessary to regard M. de Blainville’s 
dismemberment no longer as a subgenus, but as a rightful genus, which must 
* Beitrige zur Kenntniss der Corallenthiere, &c., p. 95, 1831-34; also Berlin Transactions for 
1832. 
+ Manuel d’Actinologie, p. 370, 1830-34. 
{ Ehrenberg suggests that Madrepora galaxea of Solander and Ellis, or Siderastrea galaxea of De 
Blainville, may be identical with Astrea astroites (consult Esper, Madrep. tab. 35) ; but such a generic 
determination it is considered would be inadmissible for the reasons stated in the text, and the coral 
exhibiting clear proofs of a distinct mantle between the stars (Beitrage, &c. pp. 82, 95). 
