Uur knowledge of the phytoplankton of the Pacific Ocean is still 

 incomplete and fragmentary in comparison with that of the Atlantic. As 

 far as we are aware, the number of Diatoms recorded from Japan and 

 its adjacent regions amounts in all to about one thousand, species and 

 forms, living and fossil. Most of the information has been based on the 

 material collected by European travellers in Japan. It must be admitted 

 that a great number of seasonal or local variations seem to have been 

 described as new, and that no less a number of indigenous forms have 

 been erroneously identified wnth European species. How many species 

 out of the number may be counted as valid, we are unable even to 

 imagine at present; and a considerable addition to the Diatom flora of 

 Japan may also be expected. 



Under this heading we intend to revise the Japanese forms of Di- 

 atoms, comparing them, as far as possible, with the specimens from 

 other localities. It may not by any means be an exhaustive list, but 

 it is hoped that it may give a new starting-point to the study in that 

 direction. 



The Japanese material here treated has been collected by one of us, 

 Yendo, or with the kind assistance of his friends. Observations of living 

 specimens have also been attempted whenever possible. 



I. On Chaetoceras. 



Subgen. I. Phaeoceras Gr.\n. 

 Sect. I. Atlanticae Ostenf. 



Chaetoceras atlanticum Clevk. 



Cleve: 1873 a. p. 11. Taf. 2, fig. 8, — Gran: 1906, p. 64. 

 fig. 74. — Karsten: 1905 — 7, p. 115. Taf. XV, fig. 9. — Oka- 

 mura: 1907, p. 89, pi. IV, figs. 56 — 62. — Yendo: I9i2,p.26. — 

 Meunier: 1910, p. 212, PI. XXIV, figs. 1—3. 



= C. ailanticiun var. iumescens Grun. in Van Heurck : 

 1880—85, PI. 81, fig. 6. 



