100 BRITISH FOSSIL CORALS. 



2. Thamnastrea concinna. Tab. XVIII, figs. 3, 3«, M, 3r. 



AsTREA CONCINNA, Goldfuss, Petref. Germ., vol. i, p. G4, tab. xxii, fig. la, 1826. (It 



appears doubtful whether the figures \a and 16 ought to be 

 referred to this species.) 



— MiCRASTON ? Phillips, Illustr. of the Geol. of Yorkshire, vol. i, p. 126, 1829. 



— CONCINNA, HoU, Handb. der Petref., p. 402, 1830. 



— VAEIANS, F. A. Roemer, Vers, des Norddeutscheii Oolithengeb., p. 23, tab. i, 



figs. 10, 11, 1836. 

 Agakicia lobata, Morris, Cat. of Brit. Fossils, p. 36, 1843. 

 AsTREA VARiANS, M'Coij, Ann. and Mag. of Nat. Hist., s. ii, v. xi, p. 418, 1848. 

 Synastrea CONCINNA, Millie Edwards and J. Ilaime, Ann. des. Sc. Nat., s. iii, v. xi, p. 135. 

 Stephanoc(Enia CONCINNA and Tremoccenia varians, D'Orbigny, Prod., vol. i, p. 386. 

 Thamnastrea concinna, Milne Edwards and /. Ilaime, Polyp. Palseoz., etc., 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. ?>a). 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. 3(5), and contains in general only one small 

 coliunellarian 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, Avhich 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 radise are much more numerous outside the walls of the 

 coraUites than in the visceral cavity, and in their costal portion these laminae bend so as to 

 join those of the surrounding corallites ; they pass thus without interruption from one 

 fossula to another, but usually change abruptly their dn-cction 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 thcGreat Oolite at Minchinhampton, 



' The only characters assigned by that author to A. micraston, are "calices small and equal." 



