CORALS FROM THE CORAL RAG. 95 
A horizontal section made some way down from the calicular surface shows that the 
walls remain simple, and very thin or even rudimentary, but the different corallites united 
in a common mass are always very well delimitated, and the same septa never extend into 
two adjoining visceral cavities, as might be supposed to be sometimes the case by the 
aspect of the calices. No columella exists in most corallites, and in those where some 
traces of a similar organ are met with they consist only in a few small trabicule. It must 
also be noted that although the small sepfa often bend somewhat towards the neighbouring 
larger ones, they always remain quite free at their inner edge, and that the calicular 
gemmation takes place at a considerable distance from the centre of the calice. 
The British specimens of this species which we have examined had been found at 
Steeple Ashton, Malton, and Hackness, and belonged to the collections of the Museum 
of Practical Geology, the Geological Society, the Museums of Bristol and Paris, Mr. 
Bowerbank, and Mr. J. Phillips. The same species is mentioned by Mr. Smith as 
having been met with at Stanton near Highworth, Shippon, Bagley Wood Pit, Banner’s Ash, 
Well near Swindon, and Wilts and Berks Canal, South of Bayford. It is found also in 
abundance at Lifol, in the departement des Vosges, Stenay, in the departement des Ardennes, 
and at Heidenheim, in Germany; specimens from these localities are in the collections of 
the University of Bonn, the Paris Museum, M. Michelin, &e. 
The genus Jsastrea, as already stated (p. 74), has been established for a certain number 
of corals that we formerly placed in the genus Priozastrea (p. xl), but that differs from the 
species considered as the types of this latter group, by the total absenve or rudimentary 
state of the columella, and by the corallites being separated only by a single mural lamina, 
whereas as in Prionastrea they are independent of each other in their lower part, and 
become intimately cemented together only near the calice. 
I. explanata is one of the best characterised species of this generical division. It 
differs from J. limitata,’ I. Guettardana, I. explanulata and I. Richardsoni,* by 
the size of the calices and the number of the septa. J. Munsterana’ may be distin- 
guished from it by the principal seyfa bemg thinner outwards, and becoming somewhat 
thicker towards the two thirds of their breadth mwards. In JL. polygonalis,’ I. oblonga,’ 
and L. Michelini,* the walls are much thicker. In J. /amellosissima’® the septa are more 
distant, and in J. fenuistriata” their number is twice as great. In L. Conybearii' the 
septa are, on the contrary, less numerous, and in &. serialis’’ they are very unequal and 
| Tab. xxiii, fig. 2. 
2 Prionastrea Guettardiana, Milne Edwards and J. Haime, Ann. Sc. Nat., 3d ser., t. xii, py 1SF. 
3 Tab. xxiv, fig. 3. 4 Tab. xxix, fig. 1 
5 Prionastrea Munsteriana, Milne Edw. and J. Haime, loe. cit., p. 136. 
6 Astrea polygonalis, Michelin, Icon., pl. ii, fig. 1. 
7 Tab. xii, fig. 1. 
8 Montastrea Michelini, Bainville, Dict. Sc. Nat., t. lx, p. 339. 
Astrea lamellosissima, Michelin, Icon., pl. vi, fig. 1. 
LOSS Dab vex, pfi psy lie 11 Tab. xxii, fig. 4. 
9 
2 Tab. xxiv, fig. 2. 
