xh BRITISH FOSSIL CORALS. 
indistinctly separated by superficial, narrow grooves. Columella not much developed at 
its apex; but having a tendency to become compact, and to fill up the visceral chamber 
towards its basis. Septa very thick, closely set, scarcely granulated, and very feebly 
denticulated. Dissepiments little developed. 
Typ. sp., Baryastrea solida, Milne Edw. and J. Haime, loe. cit. 
68. Genus ACANTHASTREA. 
Milne Edw. and J. Haime, Comptes rend., t. xxvii, p. 495, 1848. 
Corallum formmg a slightly convex mass, with its upper surface strongly echinulate, and 
its under surface constituting a plate, covered with a complete, thin epitheca. Gemmation 
sub-marginal or marginal. Cora/lites united by their walls, which are somewhat cellular. 
Calices sub-polygonal, with broad, spiniferous, simple, common margins. Co/umell/a rudi- 
mentary or septal. Sepéa exsert, strong, and armed with projecting spmiform teeth, the 
largest of which are situated near the walls, instead of bemg the central ones, as im the 
preceding genera. Dissepiments very numerous. 
Typ. sp., deanthastrea spinosa, Milne Edw. and J. Haime, Comptes rend., t. xxvii, p. 4995. 
69. Genus SYNASTREA. 
Milne Edw. and J. Haime, Comptes rend., t. xxvii, p. 495, 1848. 
Corallum pediculate, and increasing in breadth more than in height. | Gemmation 
sub-marginal. Corailites intimately united by their walls. Ca/ices superficial, distinct at 
their centre, but not so towards their circumference. Colwmella very small. Septa con- 
fluent, progressing from one calicular centre to another without interruption, exsert, and 
hiding the walls, over which they extend; their calicular margin almost horizontal, and 
armed with nearly equal teeth. 
Typ. sp., Synastrea Savignyi, Milne Edw. and J. Haime, Ann. des Sc. Nat., 3™° série, vol. x, 
tab. ix, fig. 12. 
70. Genus THAMNASTREA. 
Thamnasteria (in parte), Le Sauvage, Mém. de la Soc. d’Hist. Nat. de Paris, vol. i, p. 241, 1822; Tham- 
nastrea, ejusd., Ann. des Sc. Nat., 1" série, vol. xxvi, p. 328. 
Corallum having confluent septa, and most of the other characters of Synastrea, but 
forming a fasciculus of columns or thick branches, erect, and of a more or less arborescent 
aspect. 
Typ. sp., Thamnastrea dendroidea, Le Sauvage, Mém. de la Soc. d’ Hist. Nat., vol. i, tab. xiv. 
71. Genus GONTASTREA. 
Milne Edw. and J. Haime, Comptes rend., t. xxvii, p. 495, 1848. 
Corallum always increasing by successive fissiparity, and forming a convex or lobulated 
mass, of a dense structure. Cora/lites intimately united from top to bottom by their walls, 
