imperfectly -known Species of Stromatoporoids. 233 



Acfinostro7na ScJimidtii, Rosen. (PI. VII. figs. 1 and 2.) 



Stro7natopora ScJimidtii, Rosen, Ueber die Natur der Stromatoporen, 

 p. 64, Taf . V. iigs. 1,2 (1867j. 



Coenosteum massive (?). Large astrorhizEe are present, and 

 are arranged in vertical groups, each group springing from a 

 vertical axial canal. The branches of the astrorhizte are of 

 large size and very slightly subdivided, and the vertical axial 

 canals are also of remarkably large size. The skeletal tissue 

 consists of delicate, often compressed, radial pillars, of the 

 " continuous " type, placed about ^ millim. apart, sometimes 

 arranged in rows. The pillars give off a small number of 

 delicate horizontal " arms," which give rise to a network of 

 oblong or irregular meshes. Vertical sections show that 

 certain of the ])illars are larger than others (PI. VII. fig. 2) ; 

 but this feature does not appear to be recognizable in tangen- 

 tial sections. 



Ohs. This beautiful species is conclusively shown by an 

 examination of the original specimen and slides in the Univer- 

 sity of Dorpat to be a true Actinostroma. It is most nearly 

 allied to the species which I have named A. intertextum. It 

 is, however, distinguished from this by its large and quite 

 peculiar astrorhizEe, by the small size and often linear shape 

 of the radial pillars, by the fact that the network formed by 

 the horizontal " arms " consists of oblong rather than of 

 triangular meshes, and by the presence in vertical sections 

 of a limited number of pillars of larger than average size. 

 The " concentric laminaB " are also very imperfectly deve- 

 loped, and are only represented by loose reticulated fibres. 



Locality and F'ormation. Silurian (Upper Oesel group). 

 Kaugatoma-pank, Esthonia. The species has not yet been 

 recognized either in Gotland or in Britam. 



Actinostroma intertextum, Nich. (PI. VII, figs. 3-6.) 



The coenosteum has the form of a laminar, more or less 

 circular expansion, which may reach half a foot in diameter 

 and an inch or more in thickness, and which is covered 

 basally by a striated epitheca. The surface shows astrorhiza3, 

 but these are of moderate size and do not appear to be ar- 

 ranged in vertical groups. The radial pillars are " continuous," 

 slender, and placed about -g- millim. apart; they produce 

 numerous slender liorizontal " arms," the union of which gives 

 rise to a close " hexactinellid " network, the meshes of which 

 are mostly more or less triangular. The "concentric laminee " 



