114 BRITISH FOSSIL CORALS. 



We have seen but one specimen of this species ; it was very ill preserved, and had been 

 found at Comb-Down, near Bath, by Mr. Pratt. 



This fossil, as far as we are able to judge of its characters, appears to differ from all 

 other Isastrca by the tetragonal form of its calices and the small number of septa, relatively 

 to the size of the corallites. 



2. IsASTREA LiMiTATA. Tab. XXIII, figs. 2, 2«, and Tab. XXIV, figs. 4, 4a, 5. 



AsTROiTES, etc., R. Plot, Nat. Hist, of Oxfordshire, p. 88, tab. xi, fig. G, 16/6 (good figure: 



we are inclined to think, that fig. 7 represents a specimen in ■which 



the centre of the calices had been accidentally filled up, so as to produce 



the appearance of a styliform columella). 



Madrepora, J. Walcott, Description and Figure of Petref., found near Bath, p. 47, fig. 63, 



1779. 

 AsTREA LIMITATA, Lamouronx, in Michelin's Iconogr. Zooph., p. 229, tab. xciv, fig. 10, 

 1849. 

 — — M'Coy, Ann. and Mag. of Nat. Hist., s. 2, vol. 2, p. 418, 1848. 



Prioxastrea LIMITATA, Milne Edwards and J. Ilaime, Ann. des Sc. Nat., s. 3, vol. xii, 



p. 137, 1849. 

 Prionastrea LIMITATA, P. ALiMENA, and P. LuciENSis, D'Orhic/ny, Prod, de Palaeont., t. i, 



p. 322, 18o0. 

 IsASTKEA LIMITATA, Millie Edwards and J.Haime, Polyp. Palseoz., etc., p. 103, 1851. 



Coralliim massive, terminated by a flat or somewhat gibbose surface. Calices almost 

 equal in some parts, very unequal in others; the small ones usually situated in the depressions, 

 and the larger ones on the gibbose parts of the upper surface. The calices are polygonal, 

 not very deep, and terminated by a thin, straight, mural edge. The small ones contain 

 scarcely twenty septa, but in the larger ones the number of these laminae amounts to about 

 thirty, so that there appears to be in that case three complete cycla, and an incomplete 

 fourth cyclum, but the whole of the septal apparatus presents very great irregularity ; thus 

 we have often seen between two principal septa two smaller ones, one of which, more 

 developed than the other, belonged probably to the second cyclum, and the other must have 

 belonged to the third cyclum, but had no corresponding one in the other half of the system 

 so composed. AU the sejAa are thin, straight, or only slightly ciu-ved, and sparingly 

 granulated, but presenting well characterised radiate striae on their lateral surfaces. They 

 are but slightly exsert, and, far from passing from one visceral chamber to another, they in 

 general alternate exteriorly with those of the adjoining corallite. The great diagonal of 

 the large calices is about two and a half lines ; and their depth one hne ; the small calices 

 are Uttle more than one hne broad. 



This fossil was found by Mr. Pratt in the Great Oolite near Bath. Walcott mentioned 

 it having been met with at Hampton Downs. It exists also in the corresponding deposits 

 near Caen, at Langrune, Luc, and Ranville. 



