KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 I. 55 



This since long times known coraJ, so often described and figured, might seem to 

 have no need of further investigation. Still there are some points in its structure and 

 development which raay be a little closer ransacked. 



Form of polypary sphserical or tuberous, covered with calicles and coenenchyma every- 

 where and consequently with no or very little epitheca. 



Calicles. Perhaps in no Heliolitidean there exists so great a difference in size between 

 tlie calicles as in this species, as Milne Edwards and Haime already have stated in their 

 Brit. Foss. Corals pl. 47, tigs. 1«, \h, le, all from the surface of the same specimen. 

 They vary from 2 mms. to a little less than one millimeter. The theca or inner wall is 

 remarkable for its thickness, being somewhat exsert, and contrasts in this respect Avith 

 the interiör theca of Heliol. interstinctus, which is thinner and deeper indented. 



Septa. The size of the twelve septa is also much variable. Seldom they are so 

 long and attenuated as in pl. ii fig. 30 or as also Sardeson figured them. Even in the 

 same polypary all gradations may be seen (pl. iii figs. 5 — 6) from those which nearly 

 meet in the centre, ending in a sharp point (never, hoAvever, uniting so as to form such 

 an intricate network so characteristic for the nearly allied Heliol. parvistella) to such 

 which stretch only halfways from the interiör wall and leave a nearly circumscribed area 

 enclosed in the centre betAveen their ends. And lastly there are septa (pl. ii fig. 32, 

 pl. III f. 5 the right calicle) that almost remind of those in Heliol. interstinctus. In the 

 last mentioned species the septa are equalsized, but in Heliol. porosus the}' often are 

 regularly alternating short and long. Pl. ii fig. 29. It is as if they, like »Hexacoralla», had 

 tAA'0 cycles, each of six septa of different orders, but there is no cause to assume that 

 they are not co6val. We have no indication of only six septa in the young polypierite. 

 As a further distinction from Heliol. interstinctus may be mentioned that H. porosus 

 never bears the columella-like protuberance, Avhich adorns the centre of the calicle in the 

 former. 



The septa are no mere septal spines, as so often has been asserted, but are coherent 

 laraellaj, having their edges obtusely denticulated, as shoAvn in the fig. 36 pl. ii. But 

 they may also (pl. iii f. 7) have the margins fringed Avith slender curved spines or cusps 

 reaching not quite to the centre. 



The tabulce are generally regular, but also often distantiated and deviating from the 

 horizontal. 



The c.iienenchyma has poh^edric tubuli Avith rather thick Avalls and of small diameter. 



The intimate microscopic structure (pl. ii figs. 33, 34, 35) consists of three strata, 

 a very narroAv, central one enclosed AAdthin tAvo larger, of similar structure, on each side.^ 

 The central stripe is of Avhite colour, in transparent light looking black, quite as is the 

 case of Avhat I formerly have called the primary streak or primary septum, Avith Avhich 



^ Already Qdenstedt, Petrefaktenkunde i, p. 138 pl. 148 fig. löy, had observed what he calls the 

 double wall and its dividing line in Hel. porosus. Säkdeson, Tabulaten p. 267 fig. 10 has seen the stripe 

 only ia the theca and regards it as a diAiding line of the double wall. The fibrilliie he calls a »krystallinische 

 Structur». Wbissermel, Deutsche Geol. Gesellsch. 1898, p. 61 and 63, fig. 3 & 4, has seen the »Primärstreif» 

 both in the theca, the septa and the coenenchyma iu Hel. porosus, aud as he says in Hel. interstinctus from 

 Gotland, which probably not is interstinctus on account of the long septa, the fibrillae were not clearly seen 

 by him. 



