86 G. LINDSTRÖM, HELIOLITID^. 



(fio'. 31). In a longitudinal section of the calicular tube (fig. 30) therefore only a thick 

 theca is seen, unless a septal list is sectioned, as in the same figure at left, where 

 it is obliquely streaked with the elementarj? fibrilla\ The fabulce are rather distantiated, 

 horizontal or concave (fig. 28). The aureola is narrow, scarcely attaining a breadth equalling 

 half the diameter of the calicle. Its compartments are short, irregular, intermingled 

 with those of the other, close lying calicles. The coenenchyma as seen in a longitudinal 

 section consists of narrow stripes betAveen the calicles, chiefly the aureolar tubes, which 

 enclose the same kind of oblique, dovetailing traverses as in Plasra. rosa.^ 



In the theca of the calicles, represented in fig. 29, there are some lacunaj, as of 

 perforations. They are caused by fissures and attentive examination of other specimens 

 cannot detect any vestiges of perforated walls. 



The now described variety is derived from the uppermost liraestone beds of the 

 northern pai't of Gotland, from Rute, Helvi, Klints in Othem, Klinte in Boge, quarries 

 between Slite and Bal. 



In the corresponding strata of south Gotland another variety (fig. 27 — 28) occurs 

 of the same structure, only deviating in lesser proportions. It has been found in the 

 limestone beds of Sandarfve kulle, Mallgårds klint, Linde klint, Hageby in Etelhem. 



Plasmopora heliolitoides n. 



Pl. VII, figs. 32—33. 



Corallum disciform or tuberose. The calicles of 1,5 millim. in diameter have no 

 elevated margin of the theca and this is very thin. Of septa there are only the merest 

 vestiges, some calicles being perfectly smooth inside, others faintly fluted by longitudinal 

 septal lists, the septa protruding io a transverse section as diminutive tubercles. The 

 tabulce are regular, numerous. The aureola is the narrowest in the genus, only equalling 

 one fourth of the diameter of the calicle. Irregular as the compartments niay be, unequal, 

 more than double broader than long, they are well discernible and twelve, with the radii 

 starting just opposite the septal rudiments. As the calicles are much remote from each 

 other the coenenchyma is most abundant, consisting of unequal tubuli, which in a transverse 

 section are polygonal, exactly resembling those of many true Heliolitaj, but in a longi- 

 tudinal section (fig. 33) they are by far not so regular, their thecae are sinuous and crooked, 

 not parallel, and the dissepiment upon the whole horizontal, also oblique. The two calicular 

 tubes in fig. 33 have like others in the same section, not figured, arisen from the coenen- 

 chyma through gemmation. 



This species has been found in the stratum cl of Östergarn, Gotland. 



In consequence of its regular coenenchyma it could easily be confounded with 

 Heliolites decipiens, if not on a closer inspection its aureola and its more irregular coenen- 

 chyma were observed. 



^ The section fig. 30 has beside the calicular tube, at the right hand, only fragments of other calicles, 

 one at left lowest, which is bent in another direction. The feathery lines are fragments of calicular walls. 



