Kofoid. — Mutations in Ceratium. 



PLATE 2. 



Fig. 2. Dorsal view of the same chain. Labelling as in plate 1. Note the thin- 

 ning of the skeletal wall in the antapical regions. Cell III 3 is seen 

 somewhat obliquely, reducing its transdiameter. See pis. 1 and 3 for 

 its normal dimensions. X 540. 



