KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 I. 59 



walls of the theca, l}dng parallel with the snrface of the section, and consequently not 

 cut but seen »en face». This partial dilatation of the tubuli walls caused Wentzel to 

 create a new genus Pachycanalicula for these forms. I do not think that this can be 

 considered as a so fundamental diagnostic, as to be adduced for basis of a new generic 

 division. If so it should be a permanent feature in the structure of the coral, not a 

 transient or mutable one. 



The tabute are rather more scarce and more distantiated than in the other species. 

 In several specimens they are both on the superior and inferior surface covered with a 

 dense coating of minute blackish crystals (pl. iii fig. 26) probably of pyrite, and the 

 thin tabula shines in the middle between them as a white streak. It may be this circum- 

 stance that has occasioned an opinion expressed by some author that the tabulse consist 

 of two layers and the white line (the true tabula) to be their dividing line. 



The distinction in eolour between the septal and dissepimental elements are mueh 

 clearly seen in the longitudhial sections, perhaps more so than in other forms. The 

 longitudinal thecfe, septa, spines inclusive, are of a påle strawcolour, the tabulaj black in 

 transparent light, white in reflected light. This points to some chemical or even structural 

 (histologi cal) fundamental, difference, between these two elements. 



The microscopic structure (transverse section, pl. iii f. 23) consists of the fibrillae 

 on both sides of the white streak, and they stånd forth as integral parts of the theca 

 without sign of any dividing line. 



Propagation. The onlj manner I have observed is the coenenchymal gemmation, as 

 delineated in pl. iii; fig. 27, sections i — iv. It proceeds nearly in the same manner as in the 

 other Heliolitaj. In ii three new septa are already formed and part of the theca out of 

 the walls of the surrounding tubuli, in iii there are septa and scattered fragments all 

 round in the well circumscribed calicle. In iv it is nearly complete, but of oval outline. 



This species ranges from the lowest Upper Silurian into the Upper Lower Devonian 

 of Austria. It has been found copiously in the Silurian strata of the Isle of Gotland 

 from those signed a. to /. inclusive. There is some little dissimilarity between the specimens 

 from the oldest beds and those from the top, the latter having larger calicles, but it is 

 of slight signification. 



It has been found at the following Gotland localities. In the Arachnophyllum 

 stratum, a, near Wisby. In the stratum be at Atlingbo canal, Stora Carlsö, Skäret in 

 Fröjel, Gnisvärd and Vägume vik, Petesvik Habblingbo. 



In the stratum d. at Länsa, Alnäse, Dember and Ryssnäs in Fårö, Wisby, Dalhem, 

 Klef in Sundre. 



In the stratum f. at Sundre, Hoburg, Sandarfve kulle, Löjsta klint, Mallgårds klint. 

 Lilla Carlsö, Follingbo, Bara backe, Gothem, Tjelders in Boge, Slite, Wägume vik, Longume 

 and Pafvals in Lärbro, a quarry near Lärbro church, Helvig on fields, near Bunge church, 

 Alnäse in Fårö. At Lau, Bondarfve backe in Burs, Klinteberg. 



Through the kindness of the late Prof. James Hall I have received specimens from 

 the Falls of^Ohio. 



I have also examined specimens from the »Oberes Untei'-Devon : Zone Heliolites 

 Barrandei» near Graz in Austria. 



