2 Dr. G. Lindstvom on the Affinities 



was tlic first to express, that the order Tabiilata is founded 

 on a character too artificial to allow of its retention. 



The chief distinctive feature of the Tabulate Corals is stated 

 to be the jireseiice of tabuhv or floors, rejiresenting what may 

 be aptly called the horizontal element of the coral, in direct 

 opposition to the vertical elements, viz. the wall and the septa. 

 According to my views of the different ])arts of the corallum, 

 these tabular are completely homologous with the dissepiments 

 of the other corals. They consist of sclerenchyma secreted 

 by the basal parts of the animal, within the wall and between 

 the septa. In many Cyathophylloids it is very easy to see how 

 tiie vesicular dissepmients in the centre of the visceral chamber, 

 where the septa are absent, pass without the least interruption 

 into larger, elongated, faintly convex, and horizontal laminse, 

 or even into a single lamina, which, being smooth and more 

 or less horizontal, can in no way be distinguished from a com- 

 plete tabula. In longitudinal sections of the Cyathophylloids, 

 tabula} are seen in one place and small vesicular dissepiments 

 in another, at the centre of the same individual. We can thus 

 see without any difficult}' how the lateral vesicular dissepiments 

 are changed into tabula?. In some Cyathophylloids in which 

 the cup is deep there seems to exist an exception, in so far that 

 there is apparently an exterior zone of vesicular dissepiments, 

 the lamina? composing which are directed in a slanting manner 

 outwards and upwards, and which have no connexion with 

 an interior zone of horizontal tabulie. This sharp distinction 

 is due to the circumstance that those parts of the dissepiments 

 which are simultaneously formed do not lie in the same plane, 

 but are elevated at the sides and deeply depressed centrally. 

 Thus the tabulee, lying deep down centrally, are environed 

 laterally by older masses of dissepimental tissue ; and this 

 causes an apparently distinct line of demarcation between the 

 central and peripheral zones (see, for example, Edw. & Haime, 

 Pol. Foss. des Ten-. Pal. pi. viii. fig. 4 a). In other genera, 

 again, as Dijyhtjphyllumj Columnana^ and Litliostrotion^ the 

 dissepiments are in a very high degree, as it were, pushed 

 aside and the septa somewhat shortened ; whilst in other 

 genera, such as Pholidophyllum and some GystipTiylla^ the 

 dissepimental vesicles have quite disappeared, and the septa 

 are reduced to a minimum, being sometimes wholly wanting, 

 or only faintly indicated by rows of sparsely developed spines. 

 This diminution of the septa and dissepiments is of necessity 

 accompanied by an enlargement of the smooth central space, 

 which is seen at the bottom of the cup to be uncovered by the 

 septa and to be formed by the tabula. This surface is con- 

 tinued without interruption between the septa, and occupies 



