44 GILBERT C. BOURNE. 



formed. The process is comparable with the formation of 

 tabulae in the Pocilloporidse and the growth of Tubipora. 



Fowler shows in Lophohelia, as 1 do in Astrsea (fig. 16), that 

 there are pieces of calcareous tissue intercalated between the 

 peripheral ends of the larger septa, each possessing its own 

 dark centre of calcification. These interstitial pieces, to 

 which Fowler gives the value of true thecal pieces, are clearly 

 formed from the calicoblasts in the angle where the soft tissues 

 dip down between the exsert septa. That this is a region of 

 specially active coral secretion is shown by the large calicoblasts 

 found there by Fowler in Lophohelia and myself in Mussa. 

 In the highest parts of the calyx, as growth proceeds, these 

 interstitial pieces may develop keels on their inner surfaces 

 which presently project into the calyx as a new cycle of septa 

 (vide fig. 7, Euphyllia). 



The Costse. — These are clearly shown, from von Koch's 

 account of the development, and from the study of such forms 

 as Astrsea and Euphyllia, to be nothing more than the peri- 

 pheral ends of the septa projecting beyond the theca. But 

 there are structures called costse in Madrepora (Fowler) and 

 Leptopenus (Moseley) which do not correspond with the septa, 

 and clearly cannot be continuations of them. Such costse 

 alternate regularly with the septa in Leptopenus and in some 

 extinct forms (several species of Zaphrentis). In the latter 

 they are said to be epithecal in structure ; unfortunately we 

 have no specimens in the Oxford museum which illustrate the 

 point. But, from the figures of Leptopenus, I am inclined to 

 think that the so-called costse in this form are epithecal in 

 origin, formed, that is, by the representative of the " Band- 

 platte" in this form (which presumably has the same relations 

 as in Fungia). Until we know more about the development 

 of the skeleton in the Perforata, it would be rash to dogmatize 

 about the " costse" in Madrepora. 



I have treated the questions relating to the corallum at 

 length, because every fresh form that is examined convinces 

 me that the expectations formed of founding a new classifica- 

 tion of the Madreporaria on the anatomy of the polyp are to 



