CLASSIFICATORT POSITION OF SOME MADREPORAEIA. 135 



mental tissue, through which the septa jDass and from which they 

 are clearly distinguishable. This tissue assumes a concentric 

 arrangement, something like a series of rudimentary walls, one 

 within the other, as in Litliostrotion, in which genus it was first 

 placed by its first describer. Sometimes the inner ring of endo- 

 theca is more fully developed than the others, simulating an inner 

 wall ; but this is not constantly the case, or it would furnish grounds 

 for the creation of a new genus." But Mr. Tomes had not read 

 carefully the description of the species in the ' British Fossil Corals ' 

 and in the Hist. Nat. des CoraU. vol. ii. p. 529 by Milne-Edwards 

 and Jules Haime. In the first-mentioned work is stated, " The 

 dissepiments, which in many specimens have disappeared completely 

 or have been more or less modified in form by fossilization, are ivell 

 developed, arched, somewhat decline inimrds, and situated at one 

 third or one fourth of a line apart ; some remain simple, but most 

 of them bifurcate " (p. 74). " Traverses bieu developpees,"arquees, 

 un pen inclinees, ordinairement bifurquees " (Hist. jN'at. des Coral. 

 p. 529). 



The description of the endotheea by Milne-Edwards and Haime 

 was correct and quite sufiicient for the purpose of specific distinc- 

 tion. The notion of there being a set of walls one within the other 

 is not correct, and the appearance is due to the obliquity of the 

 dissepiments and their being cut across horizontally in making 

 sections. 



The author states (p. 558) that " increase takes place in this 

 species by gemmation on the walls between the calicos, just as in 

 Isastrcea." The gemmation of Isastra'a certainly does not take 

 place between the walls of corallites, but within the calicular 

 margin; it is between the margin and the centre of a calice. 



It is also necessary to draw attention to the figure given by Mr. 

 Tomes of Isastrcea ohlonga, in which there is a very decided colu- 

 mella. It is the result of fossilization, and is similar in cause to 

 that seen in Astrocmnia major, Tomes, which is probably a Thamn- 

 astrsean, for it has synapticulse. 



" On some new or imperfectly known Madreporaria from the 

 Great Oolite of the counties of Oxford, Gloucester, and Somerset. 

 By R. E. Tomes, Esq., E.G.S. (Quart. Journ. Geol. Soc. vol. xli. 

 p. 170, 1885)." 



A few remarks are necessary on my part upon some criticisms of 

 the previous work of MM. Milne-Edwards and Jules Haime and 

 myself. 



Mr. Tomes heads a paragraph with the name Heliocoenia, makes 

 it a synonym of Placoccenia, d'Orbigny, and gives a good notion of 

 the discrepancies of opinion regarding the value of the genera. 

 Milne-Edwards, Jules Haime, M. de Eromentel, and myself do 

 not recognize the genus Heliocoenia, Etallon; d'Orbigny founded 

 Placocoenia, M. Koby associated Heliocoenia and Stylohelia. Mr. 

 Tomes difi'ers from all these naturalists and retains Heliocoenia 

 without giving any reason. In fact, if the reason for associating 



