CORALS OF THE LONDON CLAY. 31 
lamellar expansion, bent so as to shut up completely an irregular cavity, and to have all 
the calices of its constituent corallites turned outwards. The basal or inner surface of 
this lamellar corallum is coated with a thin, membranous epitheca, in which circular strie, 
indicative of its mode of growth, are perceptible. The calices are polygonal, and rather 
unequal in size; they are separated by a simple edge, which is common to the two 
adjoining corallites, and is thin where these corallites are crowded together, but rather 
thick where the reproductive process has been less active; in the latter case these mural 
edges are covered with numerous well-marked granulations, but in the former, no appear- 
ance of granulations is to be seen. Sometimes these two states are met with in different 
parts of the same specimen, but in others the whole mass presents one or the other of 
these forms, and may then be easily mistaken for distinct species. It is thus that 
M. Michelin has been led to consider the thick-walled variety as constituting a new species 
to which he has applied the name of Astrea decorata. The calicular margins present also 
at each corner a well-formed cylindro-conical columnar tubercle or process, which is not 
very thick at the basis, and is usually fluted by six or eight vertical furrows. In specimens 
that have been much rolled by the sea, these mural processes are often worn away, and 
these dilapidated Corals have also been described by paleontologists as a distinct species ; 
they constitute the Astrea cylindrica of M. Defrance. The columella is slender, cylindrical, 
and free down to a great distance from its apex, but presents at the bottom of the fossula 
vertical striae, which are produced by the prolongation of the principal septa along its 
sides, and are particularly manifest in some worn-down specimens, such as those found at 
Bracklesham, and figured in this Monograph (fig. 1 a). The septa form two complete 
well-developed cycla; a third cyclum is rudimentary in four of the systems, but well 
developed in two systems, the secondary septa of which become nearly as large as the 
primary ones, so as to give to the calice the appearance of having eight systems instead of 
six, which is the fundamental number. The eight large septa thus formed are broad, very 
thin, almost glabrous, not exsert, and terminated by regularly-arched, undivided edges ; 
the other intermediate septa are very small. The interseptal dissepiments are simple, 
somewhat concave, slightly raised towards the columella, and placed at the distance of 
about one third of a line apart. The breadth of the calice is about one line and a third ; 
the height of the mural processes two thirds of a line. 
The British fossils which we refer to this species, and which we have figured in the 
annexed plates, have evidently been modified by the long-continued action of the sea; the 
septa are much broken, and the granulations of the calicular margins are not visible ; it 
appears not improbable that the polypi to which they belonged did not live in the locality 
where these remains have been found, and that the Corals were brought there by some 
marine current. They are very rare at Bracklesham Bay, but extremely common in the 
Calcaire grossier of the environs of Paris. M. Michelin states that the same species is met 
with at La Palarea, and the Styloccenia found in this locality is certamly very similar to 
S. emarciata, but all the specimens that we have been able to examine, were in such a bad 
