ON THE BRITISH FOSSIL CORALS. 123 



It will be noticed, when specimens of Montiporinse and Madreporse are 

 compared, that the distinction is in the absence of the two large and not 

 very perforate septa in the case of the first-mentioned group, and it is clear 

 that the excessively trabecular character of its septa, coenenchjma, and walls 

 is characteristic. Moreover the Montiporinae are recent forms. 



The genus Litharcea amongst the Poritinae approaches Madrepora, however, 

 and its septa are often so lamellar that they resemble those of some Helias- 

 traeans amongst the Aporosa. Here the distinction between the forms 

 becomes limited. The two great septa are not extended to the median line in 

 Litharcea, and there is scanty ccenenchyma, but still there is some. The colu- 

 mella of Litharcea is simply formed by the union of trabeculse from the septal 

 ends. 



Now Protarcea vetusta, Hall, and Protarcea VerneuiU, Ed. & H., Lower Silu- 

 rian corals from Ohio, only differ from the species of Litharcea by having more 

 aporosesepta and some coenenchymal protuberances*. It is necessary, however, 

 on account of the comparatively late appearance (so far as our investigations 

 has as yet gone) of Madrepora and Litharcea, whilst admitting the extraor- 

 dinary relation of the last-named genus to Protarcea, to examine another of 

 the Jurassic Perforata. 



The genus Microsolena of the Poritinao carries the excessively trabecular 

 type of the Poritinae as far back as the Great Oolite ; it is of course one of 

 the extreme forms, and most remote from Madrepora. It has more or 

 less confluent septa, and nothing like the styliform columella of Protarcea. 

 Thus Pcdceacis, a form of the Madreporinfe, and Protarcea, a typo of the 

 Poritinfe, are still unsatisfactorily disconnected by intermediate species vidth 

 their allies in the secondary rocks. Eut, on the other hand, it is something 

 to be able to show an anatomical connexion between the Protarcece of the 

 Lower Silurian and the Mierosolence of the Jurassic and of the Lithara'ce of the 

 Nummulitic rocks, and between Palceacis and the Turbinarians of the group 

 Madrepora, of which Actinacis is the oldest (Lower Chalk)t. It shows that 

 the reticulate or perforate corals existed amongst the first known eoralliferous 

 rocks, that the scheme of their organization has been perpetuated to the 

 present day through many kinds of variations, but with a great break, which 

 is owing to the imperfection of the geological record. 



III. The Tabulata, which form such large portions of many modern reefs, 

 were, as has been already noticed, in existence during the Miocene+, the 

 01igocene§, and the Eocene ||. They were, of course, not found amongst 

 the deep-sea deposits of the Cretaceous period, such, for instance, as our 

 White Chalk ; but Eeuss found the genera in the reefs of Gosau. Eeliopora 

 Partschi, Eeuss, sp. ; If. raacrostoma, Eeuss, sp. ; Polytremacis Blainvilleana'; 

 P. hulhosa, d'Orb. : these are not uncommon in the reefs which were in 

 relation with the Hippurites, and the last coral genus lived during the 

 Eocene. Eeuss estabUshed a genus in 1854 for some compound, massive 

 corals, with prismatic corallites with thick imperforate walls. The calicos 

 are without radiating septa and have no columeUae. The tabulae are very 

 irregular, some being complete and others uniting obliquely with their neigh- 

 bours. The septa are represented by trabeculae. This Lower Cretaceous 

 genus he named StyJophyllum, and will be considered further on. 



* See Hist. Nat. des Corall. vol. iii. p. 185. 



t M. Lindstrom has lately described a Caloci/stis, a perforated coral from the Silm-ian. 



J See Duncan, West-Indian Fossil Corals (Q. J. Geol. Soc.) ; Eeuss, Corals of Java, &c. 



I Reuss, op. cit., and Duncan (Pal. Soc. Tertiary Corals of Brockenhurst). 



II MM. Milne- Edwards and Haimej Hist. Nat. des Corall. &o. 



