252 BRITISH FOSSIL CORALS. 



discernible from the surrounding ccenenchyma. Septa 12 in number, but little developed, 

 rather slender, and slightly unequal in size alternately. 



A vertical section shows that the visceral chamber of each corallite is limited by a thin, 

 but well-characterised ivatt, and is divided by numerous closely-set, well-developed tabula, 

 that are almost all quite horizontal. The continuation of the vertical septa is often visible 

 in the space comprised between the tabulae. The ccenencliyma is entirely made up with 

 small square cells, formed by the parieties of the vertical canalicular, and the horizontal 

 dissepiments meeting at right angles. In some parts of the corallum all those small 

 horizontal diaphragms comprised between two adjoining corallites are placed on the same 

 level, and correspond exactly; in other parts they alternate more or less completely; 

 hut in no instance do these intratrabicular dissepiments correspond with the intramural 

 tabula;. 



Found in the lower Silurian deposits at Coniston, and in the upper Silurian beds at 

 Wenlock Edge. Professor M'Coy mentions its existence at Mathyrafal, Montgomeryshire ; 

 High Haume, Dalton in F\irness, Lancashire ; Blayn y Cwm, West of Nantyre, Glyn 

 Ceiriog ; and Egool, Bellaghadereen, Mayo. A variety of the same species has been met 

 with by that geologist in the Bala limestone of Maes Meillion, south of Bala, Merionethshire. 

 Mr. Hall has also found it in the Niagara limestone, at Milwaukie, in Wisconsin. Some 

 corals from the Devonian deposits of Nehou, in Normandy, do not appear to differ 

 specifically from the former. 



Specimens are in the Collections of the Museum of Practical Geology, of the Geological 

 Society, of the Bristol Museum, the Parisian Museum, &c. 



II. megastoma is easily recognised by its large and closely-set calices, and by the 

 slight development of the ccenenchyma. 



4. Heliolites Grayi. Tab. LVIii, rigs. I, la. 



Heliolites Grayi, Milne Edwards and Jules Haime, Pol. Foss. des Terr. Palseoz. (Arch, da 

 Mus., vol. v), p. 217, 1851. 



Corallum composite, dendroidal, forming lamellar sublobated expansions, both surfaces 

 of which bear calices. These are placed at various distances from each other (one, two, or 

 three times their diameter), and are limited by a small, well-marked, circular ridge, formed by 

 the exsert edge of 12 subequal thick septa. The canalicular of the ccenenchyma are 

 somewhat irregular, and their parieties are rather thick. Diameter of the calices about 

 one third of a line. 



This fine fossil was found in the upper Silurian beds at Walsall, and belongs to the 

 Collection of Mr. J. Gray, of Dudley. 



The remarkable fron descent form of this fossil is met with in no other species of the 



