ASTROC(ENI^ OP THE STJTTON STONE. Ill 



Fossilization has rendered the original hard parts of the corals 

 very dense and white ; where there has been exposure to weather 

 the tint is reddish or rusty. The original interspaces, or the inter- 

 septal loculi, are jBlled with a more or less transparent calcite, which 

 is often coloured. Some of the septa and the columellae of some 

 corallites have been enlarged, as it were, by the accretion of dense 

 white mineral, and the swollen appearance thus given is very 

 curious. In places a deposit has diminished the diameter of the 

 cavities of the corallites. The endotheca is in small quantity, and 

 the septal laminae have parallel ridges on them, which, in longitudinal 

 sections, contrast remarkably with the dense structureless fused 

 walls which form the mural coenenchyma (fig. 9). 



This examination of a new specimen of Astrocoenia gibbosa, 

 nobis, and the reexamination of the types of the other species of 

 Astroccenia, which were described in the " Monograph of the Corals 

 of the Zone of Ammonites ancjidatus " (Pal. Soc. 1867), proves that 

 there is nothing to justify the forms being removed from the genus 

 in which they were placed by me. 



It has been shown that in the younger parts of the Astroccenice 

 the thick united walls of the adult stage are replaced by thin and 

 narrow walls, and that the calicos are shaUow and not on the top 

 of conical elevations. It has been confirmed that the septal arrange- 

 ment is peculiarly Astrocoenian, and that perfect cycles of septa 

 are not to be determined after the form leaves the young condition. 

 The gemmation of A. gibbosa has been shown to conform to the 

 Astrocoenian arrangement, and to take i^lace, not between the walls 

 (for that is impossible), but where it was stated to occur in the 

 former Monograph. The growth of a bud is shown to commence 

 within the range of the septa or at the margiii of the lumen of a 

 corallite. 



Finally there are none of the characteristic structures of StylastrcBa, 

 E. de Erom., in the Infra-Liassic forms which were described as 

 Astroccenice by me in 1867. 



DESCKIPTION OF PLATE YIII. 



Fig. 1. Astroccenia gibbosa. Duncan, part of a corallum (colony), showing the 

 walls of adjoining corallites united to form a dense homogeneous 

 mural ccenenchjma, c, except where a narrow Une between the walls 

 indicates incomplete fusion. The dark portions are interseptal 

 loculi, a. x5. 



2. Calices more or less worn. X 12. 



3. Part of a transverse section of the corallum. x3. 



4. Longitudinal view of a part of the corallum where growth has pro- 



StylLnacese, where (take the instance of Stylina Belabechii) there is a greater 

 or less amount of exothecal cellular growth between the walls of corallites. 

 The drawing of the Htylina (in Brit. Foss. Corals, Ed. & Haime, Pal. Soc. 

 Oolitic Corals, pi. xv. fig. I) illustrates this intermural cellular coenenchyma, and 

 a similar structure was admirably figured by De Wilde in the Monograph 

 on the Brit. Foss. Corals, 2ud ser. Pal. Soc. 1866, pi. vi. 



