KONGL. SV. VET. AKADEMIENS HANDLIXGAR. BAND 32. N:0 I. 17 



sort of septal grooves is formed, verv small and shallow, nearly reminding of those which 

 are seen in some Favositidai (pl. ix fig. 4). 



The genus Camptolithus makes it evident that the convex lamells of the coenen- 

 chyma in the Plasmoporinae are identical with the tabuUp of the calicnlar tube, by showing 

 how the remarkably convex tabula? of the calicle of that genus are transformed into the 

 same sort of convex lamellao as in the coenenchyma (pl. x iig. 29, 30). 



To complete the description of the different parts of a single polypierite, amongst 

 the Heliolitidaä, we may only remind of the above described coenenchyma and how it in 

 the beginning of its formation is a »border-zone» around the solitary calicle, as the case 

 is in the intracalicinal gemmation. Here it must, however, be reraarked that Theco- 

 psammia and Turbinaria, above given as instances, have only one theca enclosing both 

 the border-zone and calicle together. 



Now this condition of two thecas in Heliolites is very much in analogy with what 

 obtains in solitarj^ polypierites of several other pateozoic corals for instance in the genus 

 Acervularia where a central area is enclosed within an interiör theca ^ and around this a 

 flattened border-zone contains the septal ends and the interposed dissepiment. That in- 

 teriör wall is formed by dilatations of the sides of the septa, in such a way that the dila- 

 tations from contiguous septa meet and join, thus building up a well marked annular 

 area, enclosing the central ends of the septa. The exteriör theca or the theca proper 

 which, although very thin, envelops every individual polypierite in a compound Acervu- 

 laria, clearly indicates that the exteriör area can by no nieans be considered as extra- 

 calicinal or as an exotheca, it is indeed an endothecal structure. 



Besides Acervularia we find other corals with a similarly formed interiör theca, as 

 Pachyphyllum and Smithia, but in these thei'e exists no exteriör limitation or exteriör 

 theca between the different polypierites and where the septa of neighbouring calicles meet 

 they are confluent without boundaries and consequently form a coenenchjana between the 

 central areas of the calicles. It may be said that a coenenchyma originates as soon as 

 in a compound coral all exteriör thecas which else separate the polypierites in a colony, 

 have vanished. 



In Acervularia there is no coenenchyma, as we have seen, because every polypie- 

 rite has its own exteriör theca. In such genera again as Arachnophyllum, Pachyphyllum 

 and Smithia and several others there is a true coenenchyma in the same conception as 

 in Heliolites. In such genera the coenenchjrma must be strictly regarded as endothecal 

 or calicinal. What in Heliolites from the beginning was the calicle proper has by the 

 exorbitant development of the border-zone become but the central area of the polypierite. 

 It ought then properly be called the interiör area of the calicle, when the surrounding 

 coenenchyma is the exteriör, but for conveniences sake I have in the dcscriptive part of 

 this memoir retained the name of calicle to designate it. 



HiNDE has objected^ to my views on the analogy between the »cylindrical corallite», 

 as he says, in Heliolites and Acervularia. In the former, he writes, the wall is too 

 distinct and well detined to be compared with the »pseudowalls» of Acervularia. This 



' Muraille intérieixre H. Milne-Edwards. 

 s Geol. Mag. 1883 p, 87. 



