ASTR^OPORA. 81 



The epitheca may at any time reappear under an advancing creeping corallum. In thick 

 growths, which have died down but are being grown over by a new layer, an epitheca wliich 

 can have no connection with the original epitheca of the colony, forms under the edge of the 

 new layer. When a layer is creeping down round a globular specimen, the epitheca seeks to 

 hinder the downward movement, at times even bending up over the edge of the advancing 

 corallum, covering up the calicles. This may or may not succeed ; if not, it is because the 

 ccenenchymatous skeleton above the upper edge of the epithecal fold becomes so thick that it 

 can roll right over it. As a rule, the tendency of the epitheca is to turn the edge of a 

 corallum upwards. It appears as if the edge of the corallum can only manage to hang 

 downwards by growing faster than the epitheca, and thus rolling over. 



Dana has described the living calicles of A. profunda as having 24 (or more) tentacles in 

 two series, and as being of a brownish colour. A very common colour for the unbleached 

 corallum is a bright yellowish red or brown. 



DEFINITION OP THE GENUS. 



The genus Astrceo'pora may be thus defined : Madreporaria with a purely ccenenchy- 

 matous skeleton resting upon a basal epitheca, either spreading with the latter in expanding 

 plate-like gi-owths or rising over it to form solid masses. The ccenenchymatous skeleton is 

 composed typically of costal vertical pillars and of parallel tiers of synapticular floors. 

 The calicles with but feebly developed intracalicular septal laminaj, six only approxi- 

 mating to the centre. 



ON THE RELATION OF THE GENUS ASTR-EOPORA TO THE GENUS TURBINARIA. 



BlaiuvLlle's suggestion (' Manuel d'Actiuologie,' p. 384) that these two genera might 

 without inconvenience be united, was adopted with some hesitation by Dana. Tliis author's 

 note of interrogation, however, did not again reappear, and the two genera have been closely 

 associated ever since, the chief distinction between them being the weU-developed columella 

 of Turhinaria. 



T. stdlulata, ranked as an Astrteoporan by Blainville and Dana, but recognised as a 

 Turbinarian by Milne-Edwards, was supposed to represent a transition form. Ortmann, in 

 his genealogy of the Corals,* suggests the deduction of Turhinaria from Astrceopora. The 

 present writer t was at one time disposed to consider Astraxpora, on account of the absence 

 of all specialised method of budding, as a primitive form of ccenenchymatous coral from 

 wliich first Madrcpora, and then Aatravpora through Madrcpora, might possibly be deduced. 

 As a matter of fact, judging from skeletal structm'cs alone, all we really know, is that the 

 corallum in both Turhinaria and Asfra'opora, as also in many other genera, rises above the 

 original epitheca as a purely septal or ccenenchymatous structure. This is the only point 



• 'Beobachtung an Steinkorallen von der Siidkiiste Ceylons,' Zool. Jahrb. Systematik, iv. 

 (1889) p. 586. 



t Ann. and Mag. Nat. Hist., xv. (1895) p. 499. 



V. 



