AND GLTPHASTRJEA, DFNCAN (1887). 215 



lighter fibrous layer of calcareous material, regarded as stereoplasm. 

 Likewise the thecal wall exhibits a similar dark layer, which, in 

 Flabellum, is next the exterior and connected with the dark layer of 

 the septa, and, further, has the slighter fibrous stereoplasm on one 

 side only, that is, on the interior. In the other genera mentioned 

 above, the dark layer of the septa does not directly connect with 

 the dark layer of the thecal wall, — at all events as regards the prin- 

 cipal septa — but when present in the theca it has a layer of lighter 

 stereoplasm on both the exterior and interior surfaces. The nature 

 of this dark layer in recent corals has not yet been determined ; it 

 is known as the primary layer or centre of calcification, and appears 

 to be distinct in character from the stereoplasmic layer which 

 encloses it, though there is no well-marked line of division between 

 them. There can be no doubt that the transverse growth-lines and 

 longitudinal ridges and furrows constituting the inner layers of the 

 septal laminae and the outer layer of the theca, in Septastrea, corre- 

 spond to the darker primary layers in the recent corals mentioned 

 above. Unfortunately the fossil coral is less adapted for microscopic 

 investigation than the recent forms, owning to the incoherent nature of 

 the primary layer ; and it is only where the cornllites are now solidified 

 by stereoplasm that it is possible to obtain transparent sections. 

 These show, less distinctly however, the same minute structure as in 

 the recent corals. 



Two partially conflicting views as to the nature of the septum in 

 Aporose Corals have hitherto been maintained. Thus Edwards and 

 Haime * cursorily state that in the most highly developed septa there 

 are two parallel laminae, which are either fused together directly or 

 by an intermediate tissue. This view seems to be still held by 

 Prof. Duncan t, who says of the present form, S. Forhesi^ " The 

 septa are bilamellar and the evidence of a very irregular and narrow 

 interlamellar space is apparent, sometimes superficially and invariably 

 in microscopic sections of corallites near the calicos." 



Prof. LindstromJ, on the other hand, has advanced the view that 

 the normal septum in living and fossil corals, whether palaeozoic or 

 neozoic, consists of a narrow, central, primary lamina enclosed on 

 both sides by a layer of stereoplasm, or endothecal structure, and 

 that this primary lamina is virtually the septum and possesses a 

 difi'erent structure from the enclosing stereoplasm. This view of the 

 nature of the septum is also supported by Dr. G. von Koch§, one of the 

 foremost authorities on living corals ; Dr. Fowler || and Mr. Bourne % 



* Histoire nat. des Coralliaires, vol. i. 1857, p. 57. t Loc. cit. p. 28. 



X " Contributions to the Actinology of the Atlantic Ocean," Kongl. Svenska 

 Vetensk.-Akad. Handl. (1877) Ed. xiv. no. 6, p. 17. Also "Om de palasozoiska 

 Formationernas Operkelbarande Koraller," Bihang till K. Svenska Yet.-Akad. 

 Handl. Bd. vii. no. 4 (1882), p. 8fi. 



§ "Ueber das Yerhaltniss von Skelet und Weichtheilen beiden Madreporen," 

 Morpholog. Jahrb. Bd. xii. (1887), p. 156, pi. ix. fig. 4. 



II "The Anatomy of the Madreporaria. — III.," Quart. Journ. Micros. Sci. 

 vol. xxviii. (1877), p. 7, pi. i. figs. 4, 5. 



^ " On the Anatomy o^Mussa and Ewphyllia, &c.," ibid. vol. xxviii. p. '23, pi. iii. 

 figs. 2, 3. 



