KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 I. 83 



The sejDta are of the shortest, scavcely visible in a longitudinal section as small 

 acLilte, which also sit on the very regular tabulte. The aureola is distinct and regular 

 attaining ^U of the diameter of the calicles, those of neighbouring calicles being intermingled. 

 The coenenchyma is of the cancellate order, the tubuli with angnlar or zigzagformed walls, 

 giving in combination with the traverses a polyedric appearance to the compartments of 

 which it is composed, fig. 20. There are also dark patches, probably vestiges of the 

 tiibular walls. 



This is an exclusively American species. The Swedish State Museum possesses 

 specimens of it from Tennessee, Decatur C*^', a gift from Prof. Ferd. Roemer, from Perry- 

 ville, Cincinnati, and I.ouisville, Kentucky, a gift from Dr W. R. Head in Chicago. 



It differs from the other species through its short septal spines and the minute 

 aculfe on the tabulaj, and through its regularly cancellate coenenchyma. 



Pla-'^inoporn stella n. 



PI. v, figs. 19 — 26, 29, sections I— VII, pl. XI, figs. 30, 37. 



1854. Plasmopora petaliforrais M. Edw. & H. p. p. Brit. Foss. Cor., pl. LIX, tig. Ib, not the others; this is 



delineated from a different speciraen thau the other figures, which represent the 

 trne Plasmop. pelalifonnis. 



Corallum discoid, flat on the superior surface, as well as on the inferior one with 

 its thin, finely wrinkled epitheca. 



The calicles of little more than 1 millim. in diameter, have rather long septa, 

 consisting of large, coherent lainellfP, in the edges serrulate by irregular, upwards directed 

 spines, the lamellae being striated in the same direction. The tabulce are concave, irregular, 

 intercrossing and being secreted låter than the septa at the same height they are inter- 

 sected by these and reposing between them. 



The aureola is one of the most regular and typic. (Especially pl. xi, tig. 36.) Its 

 width is equal to ®/4 of the diameter of the calicle. The twelve compartments formed 

 by the prolongations of the septa are equalsized, wedgeshaped, a little widening outwards.^ 

 In a longitudinal section this zone is distinctly separated from the other narrow coenen- 

 chymal tubuli as broader belts, one on each side of the calicular tube, pl. xi, f. 37. 



On the outside of the theca, in some specimens (iig. 22) small cost^ are to be seen 

 between the radii of the aureola, without any connection with the interiör of the calicle. 



The coenenchyma outside the aureola consists of tubuli nearly like those of a 

 Heliolites (fig. 23 and pl. xi, fig. 37) or also more irregular (figs. 20, 22, 25). They are 

 transversally divided by regular, horizontal tabulaä which, however, sometimes, especially 

 within the aureolar zone, are modified into convex lamellaj. 



The coenenchymal gemmation has been observed as represerited on pl. v, fig. 29, 

 sections i — vii. Out of a highly irregular coenenchyma two new calicles are developed 

 in such manner that the vertical walls of the tubuli by and by concentrated on two points 

 become roughl)^ circular (iii) with some incipient septa (iv). In the left hand calicle (v) 



