Il8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



DESCRIPTION OF PLATE 4 



PAGE 



Lake Balls formed by Blue-green algae. (See pi. 5) 100 



Fig. I. (X 2.) Exterior surface of pear-shaped specimen. U. S. Na- 

 tional Museum, Catalogue No. 60690. 

 2. (X 2.) Transverse section of an ovel-shaped ball, showing 

 concentrically laminated structure. U. S. National Mu- 

 seum Catalogue No. 60691. 



These lake balls were in the process of formation by filamentous 

 algae when taken from the lake. 

 Locality: Squaw Island, Canandaigua Lake, New York. 



Layer deposit by Blue-green algae 100 



Fig. 3. (Natural size.) Botryoidal outer surface of specimen repre- 

 sented in section by figure 4. The same occurs in Collenia 

 uiidosa (pi. 13, fig. 2). U. S. National Museum, Catalogue 

 No. 60692. 

 4. (Natural size.) Vertical section thrcfugh a layer 7.5 cm. thick. 

 Compare with the section of Camasia spongiosa (pi. 12, fig. 

 i). U. S. National Museum, Catalogue No. 60692. 

 The specimen illustrated by figs. 3 and 4 is from Green Lake, 2 

 miles (3.2 km.) southwest of Kirkville, Onondaga County, New 

 York. 



