10 G. LINDSTRÖM, HELIOLITIDiE. 



hei-e (in Heliopora) is composecl of the tubes of absorbed polyps and zooids». Accepting 

 the affinity of the Heliolitidte with Heliopora, as given by Milne Edwards, Moseley con- 

 cluded, that all Tabulata were Alcyonarian and consequently that the Heliolitidge were 

 dimorphic. The contents of this iirst memoir Avas in the raain reproduced in the Chal- 

 lenger Report. He there ^ proposed the terms »autozooids» for the sexual polyps and 

 »siphonozooids» for Kölliker's zooids. These suggestions of Moseley were eagerly accepted 

 by NiCHOLSON, who 1878 in his »Silurian Fossils of Girvan» ^ says: »In view of the 

 researches of Moseley upon Heliopora we shall consider the smaller tubes (in the coenen- 

 chyma) to be really of the nature of corallites, tenanted, probably, in the living condition 

 by a peculiar kind of zooids». In his work on the Tabulata (1879) he calls the different 

 sets larger and smaller corallites and he changed låter ^ these terms in accordance with 

 Moseley into Autozooids and Siphonozooids of which the former correspond with what I 

 would call the interiör area of the calicles and the latter with the coenenchymal tubuli- 

 In this respect a few authors, as Waagen, Sakdeson and the anonymous translator of 

 Zittel's Text-book in English, have followed Nicholson. I shall revert to this below. 



Of the latest authors Wentzel is almost the only one who has paid some closer 

 attention to the structure of the Heliolitidean coenenchyma ■*. He in the main accepts my 

 views as published several years ago and establishes two types af coenenchyma, of which 

 he calls one, my vesicular coenenchyma, for costal coenenchym and the second which he 

 does not distinguish by a separate name is identical with my tubular coenenchyma. 

 One of the conclusions to which he has arrived^ is, that the coenenchyma! tubuli are 

 not to be considered as a peculiar structure, independant of the septa, but as origina- 

 ted through their furcation, coalition and again repeated furcation. "^ 



The HeliolitidaLi display in the most evident manner the two elements out of which 

 the sceleton in most corals is constructed, the vei'tical and the horizontal. The vertical 

 element reveals itself as theca, septa with septal spines, tubuli and various detached 

 formations in the coenenchyma; the horizontal element again is obseiwed as tabula» and 

 various other sorts of dissepiment. Out of variations of both these elements the coenen- 

 chyma is composed. ' In the Heliolitidaj together with the Coccoseridte it is of essentially four 

 different kinds. These are 1) the tubular coenenchyma, 2) the vesicular, 3) the bacular 

 and 4) the compact coenenchyma. 



1. The tuUmlar coenenchyma which prevails in the genera Heliolites, Cosmiolithus 

 and Proheliolites consists of narrow, mostly polygonal tubes enclosed within polyedric 

 thecaj and divided by regular horizontal tabuku (dissepiments or traverses) more numerous 

 or closely set than in the adjoining calicles. They increase by fission. 



^ p. 121. 



2 Pt. I, p. 53. 



ä Mamial of Palseontology 3<> Ed. 1889, p. 335. 



* Zur Keiintniss der Zoaiitharia tabulata, 1895, pag. 3, 7 — 12. 



" 1. c. pag. 11. 



'' Wbissermel (Zeitschr. dcutsch. Geol. Gesellsch. 1898, p. 66) has also trcated of the sceletal parts and 

 given good information. 



' There is a decided diöerence in colour between the two kinds of elements when seeu in transparent 

 light; the vertical being påle straw-coloured, the horizontal black or grey, an outward difference, which may 

 indicate some intimatc difference iu texture or chemical compositiou. 



