92 G. LINDSTRÖM, HELIOLITID^. 



It must, however, be remarked, that the figure of L. americana in the cited work shows 

 peculiar reticulations of the surface, soine of them resembling aureolas. In the photographic 

 figures in RoiMiNGER's work^ representing Lyellia americana there are no aureolas, rather 

 the same sort of costal radii starting from the calicle as in the typical Propora tubulata. 

 The only difference I at present can find between these American Lyellias and our Propora 

 tubulata is the greater distance between the calicles of the former, though not larger than 

 in the oldest above described varieties of P. tubulata. In my specimens of the American 

 Lyellias I have not been able to detect aureolas and L. parvituba certainlj' has the calicles 

 on an unaltered surface of a decided resemblance with Pr. tubulata. 



The oldest variety of Pr. tubulata has been found in the uppermost Lower Silurian 

 beds F- at Borkholra in Estonia and in the lowest Upper Silurian beds of Gotland a, the 

 Arachnophyllum bed, near Wisby. 



The typical variety occurs chiefly in the stratum cl (Wenlock limestone) in the Wisby 

 region from Westergarns holme in south to Hall, at Nyrefs udd in Tofta, Gnisvärd, around 

 Wisby in the cliffs, Lummelunds kanal, and also at Eksta, Djupvik and higher in the 

 limestone between Stjernarfve and Lefvede and south of Westergarn. 



Abroad it occurs at Wenlock in England, at Undwa in Oesel (Up. Sil.) and at Kozel 

 in Bohemia, this latter a variety with small calicles. The North American, former Lyellia 

 forms, belong to the Niagara and Upp. Helderberg groups. 



Propora euryacantha n. 



Pl. VIII, figs. 23, 26, 27. 



Corallum massive, domeshaped or tuberose. The calicles, nearlj^ 2 raill. in diam., 

 are slightly exsert, the elevated rim formed by twelve angular nodules. The septa have 

 no proper lamella but consist entirely of spines, which seen from above are flat, triangulär 

 and acuininated and slightly bent upwards. They are densely crowded and rather 

 irregular in their direction. , They vary also in their form, being club- or tongue-shaped. 

 They differ much from those in Pr. tubulata, where they are more acuminate and slender. 

 The tabulce are rather numerous, though in the specimen delineated they are rare and 

 much reraote. In some instances they are convex in the middle, being evidently disturbed 

 in their regular growth through the septal spines. The coenenc/iT/ma, as seen on the 

 surface, is of a certain vermiculate appearance with winding grooves. In transverse sections 

 (fig. 26) the free baculi, which intercross the horizontal dissepiraents, are prominent between 

 the calicles with starry sections. In a longitudinal section (fig. 27) their structure is readilj' 

 perceptible, wth their featherlike long staffs, with barbs as it were, standing ont at both 

 sides, thus indicating a disposition of the fibrillge around a central axis. The dissepiment 

 or traverses are compressed between these baculi and almost horizontal or faintly convex 

 and again ia other places of the common convex shape. 



'■ Geol. Survey of Michigan 1873—70, pl. II, f. 1. 



