100 BRITISH FOSSIL CORALS. 
2. THAMNASTREA concInNA. ‘Tab. XVIII, figs. 3, 3a, 34, 3c. 
ASTREA CONCINNA, Goldfuss, Petref. Germ., vol. i, p. 64, tab. xxi, fig. la, 1826. (It 
appears doubtful whether the figures la and 16 ought to be 
referred to this species.) ; 
— micraston? Pdillips, lusty. of the Geol. of Yorkshire, vol. i, p. 126, 1829. 
—  concrnna, Holl, Handb. der Petref., p. 402, 1830. 
— varrans, F. dA. Roemer, Vers. des Norddeutschen Oolithengeb., p. 23, tab. i, 
figs. 10, 11, 1836. 
Acaricia Lopata, Morris, Cat. of Brit. Fossils, p. 36, 1843. 
ASTREA VARIANS, M‘Coy, Ann. and Mag. of Nat. Hist., s. ii, v. xi, p. 418, 1848. 
SynasTrpa CoNCINNA, Milne Edwards and J. Haime, Aun. des. Sc. Nat., s. ili, v. xi, p. 135. 
STEPHANOCENIA CONCINNA and Tremoca@nta vartaNns, D’ Orbigny, Prod., vol. i, p. 386. 
THAMNASTREA CONCINNA, Milne Edwards and J. Haime, Polyp. Paleeoz., ete., p. 111. 
Corallum massive and varying in form; in some specimens very thick, in others thin 
and almost foliaceous, or composed of superposed layers. Basal plate covered with a 
complete epitheca, presenting numerous circular folds (fig. 3¢). Upper surface convex and 
gibbose. Calices closely set, but unequally so in different parts of the same mass, and, 
when not much crowded together, presenting round the fossula a small elevation which 
corresponds to a very delicate or even rudimentary wall, as may be seen in corallites that 
are worn down. ‘The fossula is -shallow (fig. 34), and contains in general only one small 
columellarian tubercle ; sometimes there are two. ‘The septa always constitute two 
complete cycla ; sometimes a third cyclum begins to appear in some of the systems where 
the secondary septa become almost as large as the primary ones; so that the apparent 
number of systems, composed each of a single septum, increases to 8, 10, or even 12. 
This tertiary cyclum is very seldom complete, and in general appears only in four of the 
fundamental systems. The septa are alternately very strong and thin; the thickest are 
the most prominent, and all are well denticulated along their upper edge; those of the 
first cyclum often present near the fossula a denticulation, which is placed more apart than 
the others, and bears some resemblance to a palum. A horizontal section (fig. 3c) shows 
that the tertiary septo-costal radiz: are much more numerous outside the walls of the 
corallites than in the visceral cavity, and in their costal portion these lamin bend so as to 
join those of the surrounding corallites; they pass thus without interruption from one 
fossula to another, but usually change abruptly the direction towards the middle of the 
space existing between these. 
This fossil is common at Steeple Ashton, Upware, and Malton; the corals briefly 
described by Professor J. Phillips, under the name of Astrea micraston, was found at 
Hackness, Ebberston, and in the south of England, and probably belongs to the same 
species." Prof. M‘Coy mentions having found it also in the Great Oolite at Minchinhampton, 
' The only characters assigned by that author to 4. micraston, are “calices small and equal.” 
