CORALS FROM THE CORAL RAG. 77 



exsert, granulated laterally, thick exteriorly, but thin towards their middle part, and their 

 upper edge, which is strongly arched, becomes thicker again towards the central part of 

 the visceral chamber, but does not quite reach to the columella, so that this last-mentioned 

 organ remains quite free to some distance from its upper end. Li some of these composite 

 Corals one or two corallites may be found, having the fourth septal cyclum complete, and 

 all the system equally developed. 



A transverse section shows that the icalls of the corallites are very thick, and are 

 principally formed by the corresponding part of the septa. A vertical section brings to 

 light a structure which appears to belong to all the species of the genus Stylina. The 

 tissue, which occupies the spaces existing between the cylindrical walls of the corallites, is 

 not formed solely by the costse and the exothecal laminae, as in Astrea, but is divided into 

 superposed layers, by means of prolongations from the walls which bend down in the 

 intercalicular spaces. 



Diameter of the calices, 1^ line; distance between them, 1 or 2 lines, or even more. 



This fossil is found at Steeple-Ashton, Wiltshire, and at Malton, in Yorkshire. The 

 British specimens submitted to our investigations belong to the collections of the Museum 

 of Practical Geology, the Geological Society, the Bristol Museum, the Cambridge Museum, 

 the Paris Museum, Mr. Phillips, and Mr. Bowerbank. Some fossil Corals, which we have 

 seen in M. Michelin's Cabinet, and which were found in ,the Coralline Oolite of 

 St. Mihiel, and some other localities in France, belong to the same species. 



The genus Stylina, as defined in the Litroduction to this Monograph, contains a con- 

 siderable number of species, and corresponds to no less than eleven genera, lately proposed 

 by M. D'Orbigny. These new generical divisions are founded on the differences existing : 

 1st, in the general form of the corallum, which is well known to be very variable; 2d, in 

 the depth of the interseptal loculi which that author measured by means of casts, and 

 which decreases gradually from one species to another ; 3d, in the number of the principal 

 septa, which is sometimes six, in other instances eight, ten, or even twelve, but can always 

 be easily explained by slight modifications in the development of the same number of 

 septal systems ; and 4th, in the axis of the corallites, where the columella is sometimes 

 most evident, and in other cases cannot be seen. The absence of a columella in some 

 species of Sttjlina would certainly be a character of sufficient importance to justify the 

 establishment of a generical division, were it not merely an accident dependent on the 

 process of fossilisation, or some other cause independent of the structure of the corallite ; 

 but in many instances that is the case. Sometimes, however, we have not sufficient 

 grounds for explaining in this manner the absence of the columella, and we therefore have 

 provisionally adopted the genus Cijathophora of M. Michelin, containing the Sfi/Jina that 

 show no traces of that organ -^ but the divisions founded on the various combinations of 



1 See our above-mentioned Memoire in the ' Archives du Museum,' vol. v, p. 58. 



