PLATE I 



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Fossil Blue-green Algae (Walcott). 



A. Camasia spongiosa x 350. A blue-green alga from the Algonkian Limestone. Chain of 



cells as photographed and partly outlined. 



B. The same, higher magnification x 1400. Outline sketch. 



C. A group of seven supposedly round cells from the Algonkian Limestone as they occur 



free in the matrix x 350. U.S. National Museum, Catalogue No. 60722. 



D. The same, touched and outlined. 



E. A blue-green alga (Schizothrix) from a recent calcareous deposit at Green Lake, 



Onondaga Co., New York, x 350. For comparison. 



F. Photograph of same after treatment with hydrochloric acid. 



G. Outline drawing of another chain x ca. 1200 from a recent calcareous deposit, after 



treatment with hydrochloric acid. For comparison. 



