22 P. T. CLEVE, NOTES ON BOM! ATLANTIC FLANOÖN-.ÖRG A SIBMS. 



Skeletonema tropicum. N. Sp. 

 Plate Yffl. Fig. 30, 31. 



"7 



This species differs from S. costatum in its larger size and numerous, closer peri- 

 pherical processes. Sagittal axis 0,oi5 to 0,038, longitudinal axis 0,oi millira. Processes 

 7 to 9 in 0,oi raillim., their lengtli 0,oi to 0,02 millim. I found this species in samples 

 from the coasts of S. America, 29° S. and 6° — 10° N. Temperature 23,8 to 27,2. Salinity 

 from 34,53 to 36,oi. Evidently a tropical neritic form. 



Thalassiosira condensata. N. Sp. 

 Plate VIII. Fig. 12, 13. 



Cellules very thin-walled, short, cylindrical, united by a single central short slim- 

 tliread to somewhat rigid chains. Valve orbicular with a central pore and a marginal 

 circlet of close small protuberances, about 7 in 0,oi millim., but else without any visible 

 structure (on ignited specimens). Zone with numerous rings. Chromatophores small and 

 rounded, along tho interiör wall of the cellule. Length 0,02 to 0,03, diameter 0,025 to 0,03 

 millim. 



The membrane is so little silicious that it, on drying, becomes deformed. 



This species was found in October 1899 at Plymouth together with several arctic 

 forms. 



