254 BRITISH FOSSIL CORALS. 



Corallum massive, hemispherical, free ; its edge thin, and its under surface slightly 

 concave, and covered with a strong epitheca wrinkled concentrically. Calices circular, 

 almost equal in size, not closely set, and terminated by a very thin, not exsert, margin. 

 Costa very slender, and meeting directly those of the adjoining corallites under an angle, 

 or else bifurcating and joining small transverse laminae, so as to constitute small polygonal 

 divisions between the calices. These costse are not closely set ; they do not always 

 correspond to the septa, and they often bear some small tubercles laterally. The calicular 

 fossulse are not very deep, and contain 12 very slender septa, which extend almost to the 

 centre, and are somewhat irregular in size. Diameter of the calices almost one line ; 

 distance between them somewhat more. 



A vertical section shows that the walls are slender, but still very distinct, and 

 apparently not perforated. The visceral chambers of the corallites are occupied by large 

 tabula that are rather closely set, and in general almost horizontal, but somewhat 

 irregular. The space between the corallites is filled up with vertical canalicular formed by 

 the costse that are well developed, and are subdivided by horizontal or slightly convex 

 dissepiments into cells of about one fifth of a line broad. 



Upper Silurian deposits at Dudley, Walsall, and Delves Green. Professor M'Coy 

 mentions its existence in the Coniston limestone of Sunny Brow near Coniston, Lancashire ; 

 in the impure limestone of Golugoed, Mendinam, Caermarthenshire ; and at Egool and 

 Bellaghaderreen, Mayo. 



Specimens are in the Collections of Mr. Fletcher and Mr. J. Gray, of Dudley ; of the 

 Geological Society, the Parisian Museum, &c. 



P. petaliformis much resembles P.follis, 1 but in this last-mentioned species the calices 

 are smaller and more closely set, and the general form of the corallum appears to be 

 constantly different. P. scita 2 is much smaller than P. petaliformis, and its septo-costal 

 radii are much more regular. 



2. Plasmopora scita. Tab. LIX, figs. 2, 2a. 



Plasmopora scita, Milne Edwards and Jules Haime, Polyp. Foss. des Terr Palseoz. (Arch, 

 du Mus., vol. v), p. 222, 1851. 



Corallum free ; basal surface slightly convex, with a lamellatcd and somewhat 

 prominent edge, and covered with a strong, wrinkled epitheca. Calices equally developed, 

 shallow, quite circular, with a thin, slightly prominent edge, and set at a distance from 

 each other that does not exceed their diameter. Costa slender, smooth laterally, set wide 

 apart, in direct continuation with the septa, and always joining directly the corresponding 

 ones of the neighbouring corallites, but often united together at their outer edge by a small 

 transverse lamina, which closes up exteriorly the intercostal loculi. Septa 12, almost 



1 Milne Edwards and J. Haime, Polyp. Foss. des Terr. Palseoz., p. 223, pi. xvi, fig. 3. 



2 See tab. lix, fig. 2. 



