58 TABULATE CORALS. 



equality of the corallites in point of size, the less markedly 

 prismatic and often nearly cylindrical form of the tubes, and 

 the greater thickness of the walls. In the observations which 

 I have to make upon the structural characters of F. Forbesi, I 

 shall take the form which occurs in the Wenlock Limestone of 

 Britain and Sweden as the type of the species, and I shall con- 

 sider the variations of this type as constituting three distinct 

 varieties — viz., van Wald^^onensis, Nich., Eifelensis, Nich., and 

 tiibcrosa, Rom. It is possible that Calamopora For best, van 

 discoidea, Roemer (Sil. Fauna of Tenn., p. 19, PI. II., figs. 10- 

 10 b), is a fourth variety ; but as I possess no examples of this 

 form, I am unable to offer any opinion on this point. 



The normal form of F. Forbesi, E. and H,, occurs abundantly 

 in the Wenlock Limestone of Britain, and has been very well 

 illustrated by Milne- Edwards and Haime in their great work 

 on the British Fossil Corals (PI. LX., figs. 2- 2 g). The most 

 noticeable point about this form is the marked difference be- 

 tween young and old examples in the relative sizes of the 

 corallites — supposing, as I think may safely be done, that 

 the specimens in question really represent nothing more than 

 different stages of growth. Young examples (PI. II., fig. i) 

 are discoidal, with an inferior epitheca ; or they form globular 

 masses, which envelop parasitically the stem of a Crinoid or 

 the branch of some dendroid coral, and have their entire 

 free surface covered by the calices. The large-sized calices 

 are both exceptionally numerous and exceptionally large, their 

 diameter varying from a line up to close upon two lines, 

 while the smaller calices are usually from a quarter to half a 

 line in diameter, and are intercalated in comparatively scanty 

 numbers in the limited spaces left between the large corallites. 

 Transverse sections (PI. II., fig. i b) of such specimens show 

 precisely the same features. On the other hand, full-grown 

 examples have the form of hemispherical, spheroidal, or cla- 

 vate masses, generally two or three inches in diameter, and 

 the inequality of the corallites is much less marked than in 

 the young state (PI. I., fig. 7). There is a greater propor- 



