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DESCRIPTION OF PLATE I. 



Page. 



Atikokanu lawsoni Walcott 21 



Fig. 1. — Natural size. A naturally -weathered cylinder or pil>© 

 that is silicified in its limestone matrix. This shows 

 quite clearly the central cavity at the summit, also 

 where it is cut across below by the erosion of the 

 specimen. U.S. National Museum, Catalogue No. 58313. 

 Geological Survey, Canada, CataloRue No. 8059a. 

 " 2. — Enlargement x 6. of a portion of the weathered section 

 in Fip;. 1, which shows the walls of the tubes with 

 pores at a, also somewhat irregular septa crossing 

 the tubes. 

 " 3. — Enlargement x 3, of the upper surface of Fig. 1. 



4. — Natural size. A weathered specimen where erosion has 

 worn down into the central cavity. U.S. National 

 Museum, Catalogue No. 5831-1. Geological Survey, 

 Canada, Catalogue No. 8059b. 



5. — Natural size. An oblique transverse section, cutting 

 across the central cavities of two individuals that 

 occur side by side. U.S. National Museum, Cata- 

 logue No. 58315. Geological Survey, Canada, Cat- 

 alogue No. 80>9c. 



