STROMATOPORA TYPICA. 171 



show a singular resemblance to corresponding sections of Actino stroma astroites, 

 von Rosen, sp. 



Owing to the imperfect development of the horizontal elements of the skeleton 

 as distinct structures, " concentric laminae," in the strict sense of the term, can 

 hardly be said to exist, the skeletal tissue being thoroughly reticulate. Tangen- 

 tial sections (Plate XXII, fig. 1) exhibit a close calcareous network, traversed 

 horizontally or more or less obliquely by the branching astrorhizal canals, and 

 pierced by close-set oval or circular pores, representing transverse sections of the 

 zooidal tubes. On the other hand, vertical sections (Plate XXII, fig. 2) show that 

 each latilamina consists of a series of closely arranged slightly flexuous radial 

 pillars, which probably run from the bottom to the top of the latilamina without a 

 break, though they are necessarily so cut in sections as to appear to be more or 

 less discontinuous. The radial pillars are connected at intervals by irregularly 

 developed horizontal processes, but their individuality is not thereby destroyed. 

 Vertical sections, also, always show very distinctly developed and freely tabulate 

 zooidal tubes, which, like the radial pillars, are probably really continuous from 

 the bottom to the top of each latilamina. 



I have never seen a British example of S. typica in the " Caunopora-state." 

 Prof. Ferdinand Roemer has, however, presented to me an example of this species 

 from the Drift of Northern Germany, in which the skeleton is traversed by 

 numerous minute " Caunopora-tubes." I have given a figure of a portion of the 

 surface of this specimen (Plate XXI, fig. 11), from which it will be seen that, 

 in this case, the "Caunopora-tubes" probably belong to a species of Aulopora. 

 Professor Lindstrom, moreover, has recently shown (' Bihang till k. Svenska Vet. 

 Akad. Handlingar,' Bd. xv, Afd. iv, No. 9, 1889) that the curious fossil described 

 by Kunth under the name of Prisciturben is really a kind of " Caunopora," in 

 which the imbedded tubes belong to a Cyathophylloid coral. The original 

 specimen of Prisciturben was derived from the Wenlock Limestone of Sweden 

 (apparently from Gotland), and was supposed by Kunth to be a peculiar type of 

 Coral (" Beitrage zur Kenntniss fossiler Korallen," ' Zeitschr. d. deutsch. geol. 

 Gesell.,' 1870, p. 82). Lindstrom, however, has shown that the supposed 

 " coenenchyma " of Prisciturben is really a mass of Stromatopora typica, v. Rosen, 

 imbedded in which, as in a matrix, are the cylindrical tubes of a Cyathophylloid 

 coral. I have carefully examined a specimen of Prisciturben which I collected in 

 the Wenlock Limestone of Oesel, and I am able to entirely corroborate Professor 

 Lindstrom's observations on this subject. 



The characters of 8. typica, throughout its entire range, remain remarkably 

 uniform ; and I am not acquainted with any definite varietal forms of the species, 

 unless the Caunopora Hudsonica of Dawson — to be spoken of immediately — should 

 be regarded as one. 



