HYDROCORALLINES— STROM ATOPOROIDEA. 39 



SYNOPSIS OF GENERA AND SPECIES. 



I. Actinostroma Nicholson. 

 Laminae consisting of a meshwork of fibers. Radial pillars more 

 or less continuous throughout, subequally spaced and generally 



Fig. 59. Actinostroma fenestratum.. 

 Actinostroma expansum, sur- Vertical section X 8. (After Nicholson.). 



Fig. 58 

 face. (N. Y. State Cab. Rep.) 



projecting on the surface in the form of granules or tubercles. In 

 vertical section the pillars and laminae form a more or less regular 

 series of rectangular meshes. Astrorhizae present or absent. Siluric 

 (rare)-Dev. 



1. A. expansum (Hall & Whitfield). (Fig. 58.) Devonic. 



Large expanding masses sometimes many feet in diameter, 



Fig. 60. Actinostroma nodulatum with horizontal and vertical sections, 

 son, Pal., Ohio. ) 



Nichol- 



slightly undulating surface with low broad mamelons, three eighths 

 to one half inch from center to center. Astrorhizae absent. 

 In Upper Devonic rocks of Iowa and Canada. 



