118 BRITISH FOSSIL CORALS. 
Genus 'THAMNASTREA, (p. xiii.) 
1. Taamnastrea Lyziur. Tab. XXI, figs. 4, 4a, 40. 
StperastreaA Lamovurovuxi, M‘Coy, Ann. of Nat. Hist., s. ii, vol. ii, p. 419, 1848. (Not 
Thamnastrea Lamourouxi, Lesauvage.) 
We have seen but a few fragments of this fossil: some were very large, irregularly 
cylindrical, and somewhat mammillose ; others were slender, and these differences must 
have given to the entire mass a general aspect somewhat different from that of the 7. 
dendroidea (or T. Lamourouxi) found near Caen, in Normandy. In the latter the columnar 
branches, which constitute the compound mass of the coral, appear to vary very small in 
diameter, however large the size of this mass may be. The ca/ices are very unequally 
approximated, and where they are the less crowded in one direction most of the septa 
assume a transverse direction. The fossula is not surrounded by a circular elevation cor- 
responding to the wall, but when the corallites have been worn down the latter becomes 
visible, and, although very thin and feebly developed, shows that the radiate lamine are 
formed by the costa as well as by the septa. The co/wmella is small, but in general well 
characterised and composed of one or two round papilla. The fossula is not deep, but 
never quite superficial. The septa form three cycla, which are often complete, but some- 
times those of the last cyclum are deficient in one or two of the systems. They are thin, 
denticulated, rather closely set, not very exsert, and somewhat unequal alternately ; most 
of them are flexuous towards the circumference of the corallites. Those of the second 
cyclum differ but little from the primary ones, but are not quite so broad ; the tertiary ones 
are much narrower and thinner ; they do not appear to incline towards each other, and 
become united at their inner edge. In some well-preserved calices very distinct paliform 
lobules are placed between the columella and the septa of the first two cycla; the primary 
ones are narrower and more central than those corresponding to the secondary septa; the 
latter do not occur in the systems where the tertiary cyclum is incomplete. Diameter of 
the calices one and a half line. 
This fossil is found at Stonesfield, and is in the collection of the Geological Society 
and of Mr. D, Sharpe. A specimen belonging to the Cambridge Museum was met with 
at Minchinhampton, and a cast found near Bath, by Mr. Bowerbank, appears to belong to 
the same species, although the calices are rather smaller and more crowded than in the 
above-described specimens. 
Thamnastrea Lyelli is very much like 7. afinis' and 7. dendroidea (or 7. Lamouroue i,’ 
! Milne Edwards and J. Haime, Monogr. des Astreides, Ann. des. Sc. Nat., s. iii, vol. xii, p. 158. 
2 It is the same fossil that Lamouroux described under the name of Astrea dendroidea, Expos. 
Method., pl. Ixxviii, fig. 6, and afterwards called by Dr. Lesauvage Thamnastrea Lamourouxi, Mem. de la 
Soc. d’Hist. Nat. de Paris, vol. i, tab. xiv. 
