46 NORTH AMERICAN INDEX FOSSILS. 



VII. Stromatoccerium Hall. 

 Ccenosteum massive, of dense, thick horizontal and concentric 

 discontinuous laminae, separated by very narrow interspaces. No 

 radial pillars. Small vertical tubes penetrate the several laminae, 

 connecting interlaminar spaces. No astrorhizae. Ordovicic. 



19. S. rugosumHall. Middle Ordovicic. 

 Hemispheric, with wrinkled concentric laminae, and faint indica- 

 tions of vertical tubes. 



Black River limestone, New York, Canada, etc. 



20. S. eatoni Seely. Lower Ordovicic. 

 Expanding masses two inches or more in thickness, surface with 



mamelons. On weathered surfaces numerous concentric rings 

 appear around the mamelons. 

 Chazy of Lake Champlain. 



VIII. Cryptozoon Hall. 

 Ccenosteum of irregular concentric laminae, traversed by minute 

 canals which branch and anastomose irregularly. No astrorhizae. 

 Camb.-Ord. 



21. C. proliferum Hall. Lower Ordovicic. 

 Grows in compressed spherical cakes a foot or more in diameter. 

 In the Beekmantown horizon of New York, etc. 



IX. Labechia E. & H. 



Expanded, with a basal epitheca, vertical pillars a series of blunt 

 tubercles in the young form, connected in adult by thin calcareous 

 plates. Differs from Actinostroma in the large 

 size of the pillars which are connected by 

 plates instead of fibers. Ord. 



22. L. ohioensis Nicholson. (Fig. 73.) 



Ordovicic. 

 Laminar or encrusting. Surface often with 



... 1 1 -r. Fig. 73. Labechia ohio- 



mamelons and with minute tubercles. Ka- gmis ^ 

 dial pillars distant, interspaces vesicular. 



Upper Cincinnati beds of Ohio, Indiana, Canada, etc. 



X. Beatricea Billings. 



Cylindrical or angulated stems, often fluted and ranging in size 

 to over ten feet in length and a foot in diameter. A central tube 



