CORALS FROM THE GREAT OOLITE. 109 



Genus Convexastrea.^ 



CoNVEXASTREA Waltoni. Tab. XXIII, figs. 5, 5<2, and 6. 



Corallum composite, massive, convex, more or less gibbose, or even dendroid. Calices 

 small, rather unequal, and more or less closely set. The parts that have been worn down 

 show that the walls are circular and the visceral chambers very narrow; but in the parts 

 that remain entire the edge of this investment is completely hidden by the septo-costal 

 lamella which are exsert and somewhat cristiform. These radii are twelve in number, and 

 constitute, therefore, two complete cycla ; they are very thick, of unequal length alternately, 

 and in general separated from those of the surrounding corallites by narrow subpolygonai 

 furrows, but sometimes one or two of them join these, and others establish an imperfect 

 confluence between the adjoining individuals. The septa become rather thin inwards, and 

 present small spiniform granulations on their lateral surfaces. There appears to be no 

 columella. Diameter of the corallites almost a line ; diameter of the mural investment 

 half a line. 



This species was found in the Great Oolite at Hampton Cliffs, near Bath, by Mr. 

 Walton, in whose collection are placed the specimens here described. The fossil which 

 Mr. M'Coy refers to the Astrea reticulata of Goldfuss, and was found at Minchinhampton, 

 may probably belong to this species. By its general aspect C. Waltoni bears some resem- 

 blance to the Gosau fossil figured by Goldfuss, but the latter belongs to the genus 

 Astrocmiia, and differs from the above-described species by its polygonal walls, its non- 

 exsert septa, and its styliform columella. 



The genus Convexastrea has been recently established by M. D'Orbigny, for a species 

 found at St. Cassian, and very well figured by M. Klipstein under the name of Astrea 

 regularise This new division is very nearly allied to Stylina (p. xxix), and may be defined 

 by the followhig characters : 



Corallum massive, astreiform, increasing by extracalicular gemmation ; calices circula)', 

 and separated from each other by circunivallating furrows, through which the costal laminae 

 do not pass (excepting sometimes low down in the corallum) ; no columella ; septa not 

 numerous, and slightly exsert. 



described in our Aloiiogiapli of the Astreidae, under the name of Sfi/linu aslmidcs, and which must now be 

 called Stijlina alveolata. (See our ' Memoir on the Palaeoz. Corals,' &c., p. .^9.) It is also to be noted, that 

 the same species has been referred by Blainville to an unrecognisable fossil mentioned by Schlotlieiui, and 

 has been named by that zoologist, Sidcrastrea cavernosa. (Diet, des Sc. Nat., vol. 1.x., p. 330, ami .Alanucl 

 d'Actinologie, p. 3/1.) 



' D'Orbigny, note, ' Sur des Polypiers Fossiles,' p. 9, 18-19. 



2 Beitr., etc. tab. 20, fig. 11. 



