178 R. F. TOMES OlS" THE GREAT-OOLITE MADREPORARIA. 



Klipstein *, or with the representations of casts of 0. portlandica f 

 and C. dendroidea % figured by M. de Promentel, will sufficiently 

 explain what is here meant. 



There is no genus of corals with which I am acquainted which 

 presents a greater diversity of appearance, according to its state of 

 preservation, than Convexastrcea ; and the only representation I 

 have yet seen which gives a correct idea of it in a perfect state 

 is the one given by Klipstein of the St.-Cassian species, to which I 

 have just referred. All the others have been taken either from 

 casts or specimens which have lost their cristiform septal costae or 

 were otherwise damaged. These peculiar septal costae are very 

 characteristic of the genus, and distinguish it from Cryptoccenia, to 

 which it bears considerable resemblance, but from which it also 

 differs in not having the summits of the corallites prominent, in 

 having the walls hidden, and in having the distal ends of the septal 

 costae passing in between the distal extremities of those of contiguous 

 calices. In their peculiar form, as well as in their connexion with 

 the septa, the costae more nearly resemble those of Holocystis than 

 those of any other genus ; but the two genera are not otherwise 

 similar. 



Convexastr^ea Waltoni, M.-Edw. and Haime, Brit. Poss. Cor. p. 109, 

 pi. xxiii. figs. 5, 6. 



It occurs, but is not common, in the Great-Oolite quarry near 

 Burford, and in the railway-cutting near Eollright, from which 

 localities I have collected specimens ; and I have a specimen picked 

 up from the surface of a field between Bourton-on-the Water and 

 Northleach, Gloucestershire, not far from the latter place, 



I have seen corals, supposed to be of this species, which have been 

 obtained from the neighbourhood of Stonesfield. These were nothing 

 more than much-worn examples of the very common Thamnastrcea 

 Lyelli. 



Genus Cryptoco3Nia, d'Orb. 



The peculiar nature of the ccenenchyma of the corals of this 

 genus is visible in all the species I have yet seen, whether from the 

 Oolite or Cretaceous formations. In all of them it forms an important 

 and conspicuous part of the corallum, filling up completely and 

 symmetrically the intervals between the corallites ; and in struc- 

 ture it must be regarded as not merely porous matter to fill up 

 with, but as a tabulated tissue from the tabulae of which the young 

 corallites spring. 



In another place § I have explained my reasons for following 

 M. de Promentel, and regarding the genus Cryptocoenia as distinct 

 from Cyailiopliora ; of this I shall speak more fully when I come 

 to the latter genus. 



* Beit, zur geol. topogr. Kenntn. ostl. Alpen, p. 293, tab. xx. fig. 11. 



t Polyp. Jurass. Sup. pi. iii. fig. 7. 



J Polyp. Cor. des Environs de Gray. pi. xiv. fig. 4. 



§ Proceed. Geol. Assoc, vol. vi. no. 4. 



