18 G. LINDSTRÖM, HELIOLITlDiE. 



objection aims only at relative distinctions, at a quantitative degree of developnient and 

 does not affect the quality. The comparison can be held up, whatever the affinities of 

 Heliolites may be. It is moreover very easy to find in longitudinal sections of Acervularia 

 that the interiör theca is inore strongly built than that of Heliolites. Hinde also says 

 that there is no evidence that the tubules in Heliolites are produced by the extension 

 outwards of the ends of the septa of the coral. Not to forget the evidence given by 

 the intracalicinal gemmation and the statetnents of Wentzel above referred to nothing is 

 more fit to prove that extension than the conditions in the Plasinoporinee. In almost 

 all species of Plasmopora, for instance Plasinopora stella, Ph xi, fig. 36, the septa 

 continne in the most distinct loanner outside the interiör theca as costa; and often, as 

 also in Propora, join the septa or costae from surrounding calicles. 



The view that the coenenchyma of the Heliolitidaj is an endothecal structure, 

 although no exteriör theca for every single polypierite is developed in the compound 

 corals, is strengthened by Avhat foUows. It is a most important fact, that in some Helio- 

 litida3 the confines of the individual polypierites are most distinctly conspicuous, though 

 the exteriör theca is wanting. The figure (pl. vi, fig. 23) of Plasmopora calyculata may 

 be consulted for this feature. There the coenenchyma is partitioned off into regular 

 polyedric spaces through softly elevated ridges, also of coenenchymatous structure, thus 

 forming well circumscribed calicular areas having the small central area (h. e. the 

 calicle proper) with the inner theca in the middle and a portion of coenenchyma around 

 it. In some of the Heliolita' from Gotland faiiit traces of dividing lines are discernible 

 on the coenenchyma. In another way, as in some specimens of Heliol. interstinctus 

 (decipiens) pl. ii fig. 11, the areas of the single polypierites are well seen as small cones 

 separated from each other through shallow grooves. Lonsdale has described^ specimens 

 of »Porites pyriforniis» (= Hel. porosus) tigs 4, 4a with regularly circumscribed calicular 

 areas. It is also possible that Paljeopora? favosa M'Coy figs 3c, 3d pl. iC of »Palasozoic 

 Fossils» represents a Heliolites with distinct caliculai* areas. These tigures belong to 

 another specimen than that figured on the same plate as figs 3, 3a — b, which represent 

 the genuine Heliol. interstinctus. In Salter's »Catalogue of the Cambridge Fossils» p. 104 

 a variety of a Heliolites is mentioned with »sunk pores» and also a »Heliol. variety with 

 depressed areas at the cell inouths». 



As a conclusion based on the above given statements and facts I cannot find how 

 Nicholson's hypothesis of the dimorphisin of the Heliolitidse is to be upheld. I have 

 attempted to demonsti'ate that the coenenchyma, strictly considered, is the integral part 

 of every calicle in a compound coral, as is most evidently shown by Plasmopora caly- 

 culata and that Propora, the near affinity of which with other Heliolitida3 cannot be 

 denied, has a coenenchyma which lends no support to the hypothesis of Siphonozooids. 

 Still more convincing proofs of the irapossibility of this hypothesis are given below in 

 treating of the coenenchymal gemmation. 



Modes of i/roit'th of the coralla. The composite corals are much variable as to 

 their shape. In some species it is constant, in others again much depending on now 



* Notes on the age of the limestones of South Devonshire, jj. 721 of Transactions Geol. Soc. London, 

 vol. v, 1840, pl. 58, fig. 4, 4a—/. 



