1908] Notes on Silurian Stromatoporoids 27 



ACTINOSTROMA TENUIFILATUM, Park<. 



For description see University of Toronto Studies, op. cit. 

 Briefly, the species is characterized by continuous radial pillars 

 and straight laminae, so spaced that about se\en of each occur 

 in the space of one mm. Vertical sections therefore present the 

 appearance of a square network. While approaching the 

 structure of the type specimen, the examples under review 

 present some differences as follows: The laminae are not evenly 

 spaced, but show more closely crowded bands alternating with 

 wider spaced portions. There is also evidence of upward in- 

 flections in the laminae— a feature which is characteristic of 

 the species next to be described. It would appear therefore that 

 the present examples are intermediate l^etween tvpical ^4. tenui- 

 P.laiuin and tvpicai ^4. injlectum. 



Localities. — Station 641, Pagwachuan River, W. J. Wilson, 

 Juh", 1^)04; Pagwachuan River near mouth, W. ]. Wilson, 

 July, 1004. 



ACTINOSTROMA IXFLECTUM, Sp. HOV. 



Judging fromi the number of specimens, this species is by 

 far the most prolific in the region. WHiile fragments only are 

 available the inference is obvious that the coenostcnm is of 

 hemispherical shape, and thai: it reaches considerable dim.en- 

 sions. Vertical sections show it to be composed of delicate 

 horizontal elements, the spacing of which is extremely variable — 

 as many as ten or as few as three lamanae occurring in the space 

 of one nim. The concentric layers are connected bv continuous 

 radial pillars which occur to the number of six or seven in a mm. 

 Instead of maintaining a horizontal direction, the laminae are 

 bent sharph" upwards at intervals of about one mm. As each 

 overlying lamina follows the same course, and as the identity 

 of the lamina is lost at the apex of the fold, the coenosteum 

 appears to be traversed by vertical colum.ns miade up of loose 

 vesicular tissue. These columns do not show the compact 

 structure of those of Nicholson's Siylodictyon, but the general 

 appearance of vertical sections is very suggestive of that genus. 

 A similar arrangement is not uncommon in different Stroma- 

 toporoids, and it is very questionable whether it is a feature of 

 generic vahie. These inflected portions doubtless represent 

 astrorhizal systems, but horizontal canals are not perceptible. 

 Owing to the upturnings of the laminae it is difficult to prepare 

 sections which follow the course of the pillars over any con- 

 siderable extent, in consequence one may easily mistake this 

 species for a Claihrodictyou. 



Tangential sections do not reveal any astrorhizal canals, 

 nor is the preservation sufficientlv good to reveal the whorls 



