1915- No. 8. 



JAPANESE DIATOMS. 



Chaetoceras sp. 



Hesides tlie species of Chaetoceras treated above, we found three 

 different kinds of resting-spores of which we were unable to determine 

 the species. They were as follows. 



No. I. Size of spores extremely variable, measuring 8 u — 31 a in 

 diameter; primary valve nearly hemispherical in the smaller specimens 

 gradually complanatcd in the larger, with long slender spines all over 

 the surface. The spines reach almost to the valve-wall at the extremities, 

 where they bend more or less in a hooked form ; minute processes are 

 found on the margin of the girdle, arranged in series at nearly equal 

 intervals. Secondar)- valve greatly convex in the smaller specimens, 

 gradually complanatcd in the larger, with long and slender spines from 

 the summit, and minute processes on the rest of the surface. Very pro- 

 bably, belonging to CJi. distans, but doubtful. 



No. 2. Shape of frustules, though insufficiently known, more or less 

 resembling C af/inc Latd. Primary valve round, with minute short 

 spines over the surface. Secondary valve humped nearly as high as 

 the primary, with spines radiating from the entire surface. Some of the 

 spines reach to a special mantle consisting of the thickened girdle of 

 the mother- cell. 



A special mantle to resting-spore such as found in the present 

 specimen, is also known to occur in (\ curviseium Cleve. In the latter, 

 however, the spore-wall is perfectly smooth. 



Ostenfeld (191 2, p. 5) states the variability of the resting-spores of 

 C shnplex Ostknk. and gives a series of figures drawn by Paulsen. 

 In his species the spores seem to have the secondary valve sometimes 

 absoluteh' smooth, and sometimes with many minute spines, and inter- 

 mediate forms connecting the two forms. Whether the spores of C. 

 curvixetum Cleve mav under<jo a similar sort 



of variation, so that our spores would indicate an ^y^-j 

 extreme case, we cannot say at present. Other Ç>M 

 specimens collected at a different season, are 

 needed to solve the question. 



No. 3. Frustules unknown. Spores disc- 

 shaped, elevated in the middle on both valves, 

 erect spines of nearly equal height on the secon- 

 dary valve. Resembling to a certain extent C. 

 {Gomothecium) navicula Brightw. Cf. Ehren- 

 berg: 1854, Taf. 18. fig. 105. 



2 

 Fig. 15. Spores ci\' un- 

 known origin. X 360. All 

 from burnt preparations. 



