110 PEOP. P. MAPvTIN DUNCAN ON" THE 



AsTEocoENiA PEDimcTJLATA, nobis, op. cit. p. 20, pi. V. figs. 7-9. 



Mr. Tomes further states (p. 371) that he is only acquainted 

 with this species "through Prof. Duncan's figures, and a very 

 cursory inspection of the type specimen ; " but he places it in the 

 genus Stylastrcea. The form has none of the characters of the last- 

 named genus, and the space between the calices is not filled 

 up by thin walls with intermediate coenenchyma, but by thick walls, 

 united inseparably and without any exothecal structure between 

 them; therefore the description I gave of the form is correct 

 and the classificatory position also. Astrocoenia pedunculata, closely 

 allied to A. parasitica, nob., remains a member of the Infra-Lias 

 fa-una. 



Finally Astrocoenia favoidea, nob., is singularly Astrocoenian, and 

 the narrow united walls and polygonal calices are characteristic. 



Conclusion. 



The whole of the specimens of Astroccenice which have been 

 noticed in this communication, and all the others which were de- 

 scribed in the Palseontographical Society's Monograph already alluded 

 to, have the generic characters of Astroccenia well shown. The pris- 

 matic corallites united by their thick wallsTin the adult condition, 

 the small calices usually polygonal in outline, the essential styloid 

 columella, and the number of alternate long and short septa, are 

 easily recognized. 



The character of the costse is that of typical Astrocoeniw, and as 

 the width of the inter calicular walls varies, so the length of the 

 costse is not the same everywhere. The gemmation is either just 

 within the calice or on the top of the wall close by (fig. 8). 



In no instance are the walls joined by exothecal structures. 

 There is no coenenchyma between the walls. The septa are not in 

 an}^ cyclical arrangement, and several septa are not seen between 

 two long ones which reach the columella. In no instance have 

 the calices conical crateriform shapes and raised thin and projecting 

 margins. There are none of the special generic characteristics of 

 Stylastrcea or of Stylina present. 



- It appears that, owing to greater or less vigour of growth and to 

 the influence of crowding, the corallites may be perfect hexagonal 

 prisms, or irregularly polygonal in transverse section, and that the 

 walls of corallites in the same corallum may be very thin at the 

 calicular surface and thick lower down, or thick at the calicular 

 surface and forming with their joined neighbours a mural or 

 intercalicular coenenchyma of varying width (figs. 1-5) *. 



^ These joined walls form mural coenenchyma, and it resembles that of 

 PociU&pora and some of the Oculinidae, especially of the base of Amphihelia 

 and the stem of Astrohelia, figures and explanations of some of which were 

 given by myself in 1865, and long previously by Milne-Edwards and Jules 

 BTaime (Introductory Monograph, Pal. Soc. 1865-6, pi. iii. figs. 8, 9; Hist. 

 Nat. des Corall. vol. i. pi D, 1. fig. 8 a). The term mural coenenchyma and 

 its equivalent intercalicular coenenchyma were used by those authors in 1857. 

 It is totally distinct from the intermural coenenchyma of such forms as the 



