30 



BRITISH FOSSIL CORALS 



at once, and it even possesses the curious transverse arrangement of the vi^alls of some 

 calices which renders the comprehension of Reuss's sixth figure rather difficult. 



The Astroc(E7ii(s have been fully considered in the ' Monograph of the Liassic Corals ' 

 (PaL Soc, 1867). 



Astrocwnia decaphjlla is a rather variable species, on account of the preponderance or 

 deficiency, as the case may be, of ccenenchyma. The size of the costse is limited by the 

 ccenenchyma, and when this is very deficient they are almost rudimentary. 



There are ten principal and ten secondary septa; the secondary are the smallest, and 

 do not reach the styliforra columella like the primary. They are slightly spined towards 

 their inner margin. The costse are small. The columella is well developed, and is 

 essential and styUform. The shape of the calices varies ; in some places they are 

 circular, and in others polygonal. 



Locality. Haldon. In the Collection of WilUam Vicary, Esq., F.G.S., Exeter. 



The British specimens are not to be distinguished from those of the Hippurite Chalk 

 of Gosau, or of the Craie tufFeau of Corbieres. 



Astrocoenia decaphjlla was a very persistent form. It resembles in some of its peculiar 

 structures the Astrocoenias of the Lias, and a specimen from the Miocene coralliferous 

 strata of Jamaica^ cannot be distinguished from the form from Gosau. 



Genm — Isastr^ea. 

 IsASTR^A Haldonensis, Dunccm. PI. XI, figs. 7 and 8. 

 The corallum is hemispherical. 



The calices are large, irregular in size, very deep, and rather quadrangular. 

 The wall is thin. 



The septa are crowded, small, long, and there are five cycles of them in the largest 

 calices. 



There is a disposition to serial growth in some calices. 

 Diameter of the largest calices, nearly \ inch. 



Localifif. Haldon. In the Collection of William Vicary, Esq., F.G.S., Exeter. 



The depth and size of the calices, their thin walls, and the numerous septa, distinguish 

 this species, whose closest allies are Isastraa lameUosisshna, Michelin, sp., from the Craie 

 tufFeau of Uchaux, Isastraa Haidivgeri, Ed. and H., from the same formation at 

 Piesting, in the Eastern Alps, and Imdrcea tcmiistriata, M'Coy, sp., of the Inferior 

 Oolite. 



1 Duncan, "West Indian Corals," ' Quart. Journ. Geol. Soc.,' Nov., 1863, vol. xix, page 440. 



