74 MINNESOTA BOTANICAL STUDIES. 



clavate at distal end, suddenly attenuate at the base into a brief 

 stipe ; holdfast disc-shaped ; cells spherical, solitary or in groups 

 of two, four or rarely three, 4-16 mic. in diameter. Attached to 

 rocks at lake bottom. 



BIBLIOGRAPHY. 



Chodat, R. Bull. 1'Herb. Boiss. 5: 939. pi. 23. 1897. 

 Chodat, R. Algues vertes de la Suisse, 112. pi. 49, 52. 1902. 



EXPLANATION OF PLATE XVI. (IN PART). 



Figures i, 2, 3. Plants one half natural size. 



4. Diagram of transverse section. 



5. Cross-section of thallus, X 235. 



6. Longitudinal section of thallus showing fold, X 120. 



7. Longitudinal section of thallus, x 235. 



