116 BRITISH FOSSIL CORALS. 



of the fourth cychim, and in other instances the irregularity becomes still greater, two small 

 and almost equal septa being situated between two principal ones. The diameter of the 

 calices is not quite two lines. 



This fossil was found in the Great Oolite at Comb-Down, near Bath, by Mr. Pratt. 

 Mr. M'Coy has met with specimens of the same species in the Inferior Oolite at Dundry, 

 and near Bath. 



Isastrea explanulata is remarkable for the rudimentary state of the walls and the shal- 

 lowness of its calices. 



4. Isastrea serialis. Tab. XXIV, figs. 2, ^a. 



Corallum massive, terminated by a flat or slightly convex surface. Calices of very 

 unequal size ; in general elongated, gemmating near the margin, and forming sometimes 

 short series where two young individuals are thus produced at the same time from two 

 opposite points of the parent calice. Walls thin, compact, irregularly polygonal and not 

 projecting much between the calices. The latter rather shallow. No distinct columella. 

 Septal systems developed in a very irregular manner, and scarcely recognisable. In the 

 large calices which have not yet begun to gemmate, the number of well developed septa 

 amounts often to fifty ; they are thin and very unequal in size ; most of the small ones 

 become united to a neighbouring large one along the inner edge, and form with it a very 

 acute angle. The principal septa are often bent near the inner part ; they appear to have a 

 denticulated edge, and the lateral surfaces somewhat granulated. Between each of these a 

 very small but quite distinct rudimentary septa is always seen. 



Long diagonal of the large calices about three lines ; depth one line. 



The unique specimens of this species that we have seen was found at Comb-Down, near 

 Bath, by Mr. Pratt, and given by that palaeontologist to the Museum of the Geological 

 Society. The fossil which Prof. M'Coy^ mentions as having been found at Minchin- 

 hampton, and refers to the astrea conjluens of Goldfuss, belongs probably to the same 

 species of Isastrea. 



I. serialis very much resembles /. Lotliarivga^" but differs from it by its flat, low form, 

 the number of its septa, and the delicacy of these laminae. In /. Munsterana^ which is 

 also nearly allied to the preceding species, the septa are thicker towards their inner edge. 



At first sight the genus Isastrea appears to be very different from the genus Lato- 

 meandra^ ; but these two groups are in reality closely allied, and the passage between them 



1 Ann. of Nat. Hist., s. ii, v. ii, p. 418, 1848. 



^ Menndrina lothurinya, Michelin, Icon., pi. xxii, fig. 2. 



' Prionastrea Munsteriana, Milne Edw. and J. Haime, Ann., vol. xii, p. 13G. 



* D'Orbijjuy, Note Sur des Pol. Toss., p. 8, 1849. (lutrod., p. x.xxiv.) 



