98 G. LINDSTRÖM, HELIOLITID^. 



Propora? amhigua n. 



Pl. X, figs. 22 — 24. 



Corallura disciforra, with concentrically wrinkled epitheca. Calicles with low, only 

 faintly indented margin and very short septa, which are not visible in a longitudinal 

 section. Seen on the surface the coenenchyma resembles almost that of a Heliolites, 

 consisting of a regular reticulation of polyedric tubuli. These seeming tubuli are, however, 

 as seen in a longitudinal section only convex lamellte cut transversally and causing this 

 false appearance and there are no tubes. There is instead a vesicular tissue, quite of the 

 same nature as that usual in the genus Propora. The convex lamellaj are larger than 

 else, have some sparse acula^ on their culraen, and at certain distances there has been a 

 sort of fasciai' formed through a concentration of the lamellaä and a richer growth of the 

 aculfe. This is especiallj'' remarkable near the surface, Avhere the tabulte and the coenen- 

 chymal elements follow so closely upon each other as to form a nearly compact mäss. 

 This concentration seems here to depend entirely upon an abnorraal growth and is by 

 no means of such a regular recurrence as in Heliolites fasciatus. 



The real systematic place of this species may be contested and I have therefore only 

 hesiatingly united it with the Proporaj. It has been found in several specimens in detached 

 pieces from the Arachnophyllum stratum n near Wisby and at Skälsö, north of Wisby. 



There are still some specimens of Propora left undescribed and undeterminated until 

 raore material can be coUected. On plate ix, figs. 33 — 34 a speciraen of Propora has been 

 delineated, the only one found, which has not been placed in any of the described species. 

 It is remarkable for its exceedingly large calicles, measuring nearly 4 millims. in diameter, 

 the largest known in the whole group of the HeliolitidaB. The coenenchyma is scarce 

 consisting of large bladders and in so far resembling Pr. speciosa, but there are vestiges of 

 large septal spines, what on the other hand should approach it to Prop. bacillifera. It is 

 Lower Silurian from Alfaret, weast of Hulterstad, Öland. In the lowest Upper Silurian 

 stratum of Gotland, the Arachnophyllum stratum, which has been so fertile in many 

 different species of Heliolitidas, some Proporas have also been found, that cannot be referred 

 to any of the known species. So for instance there is one with short and stout septal 

 spines reminding of those of Pr. tubulata, but the much remote calicles are surrounded 

 by a coenenchyma of the most elementar nature, only of transverse, convex lamella?, 

 without the least traces of acula^ or other vertical elements. 



As appertaining to Propora Milne Edwards and Haime have^ with some doubt cited: 



1. Propora? acerosa E. & H. (= Porites acerosus Eiciiwald, Zool. specialis, t. 1, 

 p. 183). It is no Propora, but according to the figure in Eichwald's Lethaja rossica, pl. 

 26, hg. 4, it is a Favosites and is there by him renamed as Archajopora acerosa. 



2. Propora? cyclostoma E. & H. from the Mountain Limestone of England, a doubtful 

 species founded on Hydnophora? cyclostoma Phillips, Geol. of Yorkshire, p. 202, pl. 2, 



> Pol. terr. pal., p. 225. 



