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 stria?, 

 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 mmal 

 edges are covered with numerous well-marked granulations, but in the former, no appear- 

 ance of granulations is tc 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 palaeontologists as a distinct species : 

 they constitute the Astrea cylindrica of M. Dcfrance. The columella is slender, cylindrical, 

 and free down to a great distance from its apex, but presents at the bottom of the fossula 

 vertical stria?, 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 certainly very similar to 

 S. emarciata, but all the specimens that we have been able to examine, were in such a bad 



