320 Prof. H. A. Nicholson on some new or 



Hence vertical sections (PI. VIII. fig. 5) assume a 

 characteristic latticed aspect. In A. stellulatum, on 

 the other hand, the concentric laminae are from | to 

 £ millim. apart. 



c. The radiating astrorhizal canals are much less deve- 

 loped than they are in A. stellulatum. Hence vertical 

 sections do not markedly exhibit the large rounded 

 apertures produced by the cutting across of these tubes, 

 such apertures forming a conspicuous feature in similar 

 sections of A. stellulatum. 



Formation and Locality. Apparently common in dolomitic 

 limestones of Devonian age, Lake Winnipegosis, Canada 

 [coll. Geol. Survey of Canada) . 



Actinostroma Whiteavesii, Nich. (PI. IX. figs. 3 and 4.) 



The coenosteum in this species is massive and hemispherical 

 in form, with an imperfect latilaminar structure. The skeletal 

 laminae are undulated in such a manner as to give rise to low 

 and broad eminences, which are placed about 8 millim. apart. 

 These eminences represent the points where the astrorhizaj 

 open on the surface ; but these structures are peculiar in so 



Fi^. '2. 





Portion of the exfoliated surface of one of the laminae of A. Whiteavesii, 

 Nich., enlarged twice, showing the superficial eminences and the 

 rosette-like openings of the astrorhizal canals. Devonian, little Red 

 River, Canada. (Coll. Geol. Survey Canada.) 



far that they are entirely circumscribed and do not appear to 

 send out any radiating horizontal branches. Each astrorhiza 

 in fact consists simply of a group of short vertical canals, of 

 larger calibre than the ordinary zooidal tubes, which open in 

 a rosette-like cluster at the summit of the eminences above 

 spoken of, the canal-apertures often having a distinctly radial 

 arrangement (woodcut, fig. 2). 



