116 BRITISH FOSSIL CORALS. 
of the fourth cyclum, 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. 
A, IsasTREA SERIALIS. Tab. XXIV, figs. 2, 2a. 
Corallum massive, terminated by a flat or slightly convex surface. Cadlices 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 imer 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 paleontologist 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 confluens of Goldfuss, belongs probably to the same 
species of Jsastrea. 
T. serialis very much resembles I. Lotharinga,’ but differs from it by its flat, low form, 
the number of its septa, and the delicacy of these lamine. In L. Munsterana,’ which is 
also nearly allied to the preceding species, the septa are thicker towards their inner edge. 
At first sight the genus Zsastrea 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. i, p. 418, 1848. 
2 Meandrina lotharinga, Michelin, Icon., pl. xxii, fig. 2. 
3 Prionastrea Munsteriana, Milne Edw. and J. Haime, Ann., vol. xu, p. 136. 
4 D’Orbigny, Note Sur des Pol. Foss., p. 8, 1849. (Introd., p. xxxiv.) 
