{mperfectJij-hnoion Species of Stromatoporoids. 13 



Astrorhizgs maj be present, but were not seen in the speci- 

 mens examined. 



Ohs. This species is distinguished by its straiglit unin- 

 flected laminfe and straight radial piHars. The interlaminar 

 spaces are therefore not subdivided into rows of vesicles, as is 

 usual in the species of ClathrocUctyon. The comparative 

 remoteness of the laminae is also a good distinguishing cha- 

 racter, the interlaminar spaces being wider than in any other 

 type of the genus known to me, with the exception of G. cellu- 

 losum. Judging from the figures and description given by 

 Dr. Freeh of a Devonian Stromatoporoid which he lias named 

 Stromatopora philoclymema (" Die Korallenfauna des Ober- 

 devons in Deutschland," Zeitschr. d. Deutschen geol. Gesell. 

 Jahrg. 1885, p. 118), I should be inclined to believe that this 

 would prove to be a species of Glathrodictyon^ and that it 

 would probably be nearly allied to the present species. 8. 

 pMlodyynenia, Freeh, is, however, described as having laminae 

 decidedly further apart than is the case in G. laxiim, the 

 interlaminar spaces being stated to have a width of -^ to f 

 millim. Moreover, the tangential section of the former is very 

 unlike that of the present type. 



Specimens of G. laxum sometimes occur with " Caunopora- 

 tubes " traversing the coenosteum, and in one such specimen, 

 submitted to me by Dr. George J. Hinde, these tubes exhibit 

 well-marked septal spines. 



Formation and Locality. Corniferous Limestone, Port Col- 

 borne, Ontario. Also in the same formation, at Kelley's 

 Island^ Ohio. 



Glathrodictyon retiforme^ Nich. & Mur., sp. 

 (PI. III. figs. 6-8.) 



Stylodictyon retiforme, Nicliolson & Murie, Journ. Linn. Soc, Zool. 

 vol. x'iv. p. 222, pi. iii. figs. 1-3. 



Coenosteum massive (?) ; the under surface unknown ; the 

 upper surface (PI. 111. fig. 8) covered with conspicuous, pointed, 

 conical " mamelons," which are from 1 to 2 niillim. in height, 

 and about 3 or 4 millim. apart. The surface also is thickly 

 studded with small round tubercles, representing the upper 

 ends of the radial pillars. 



As regards internal structure, the coenosteum is essentially 

 composed of sharply undulated concentric lamina3 ; but the 

 continuity of the undulations of these is interfered with by the 

 large development of the astrorhizal systems. Each of these 

 systems consists of a vertical wall-less canal, which is sur- 

 rounded by loose reticulate tissue, this being, in turn, enveloped 

 in a series of from two to five concentrically disposed lamina3. 



