54 CLEVE, PLANKTON FROM THE INDIAN OCEAN AND THE MALAY ARCHIPELAGO. 



Diatomaceae. 



Bacteriastrum hyalinum Laudeu. 



The form I consider to be Lauder's B. hyalinum is remarkable for its short, closely 

 connected cellules, the awns of which are very delicate, furcate and close. The chains 

 occur surrounded by slime. The cell-contents have numerous small chromatophores and 

 a central nucleus. Diameter 0,o2 to 0,o25 mm. 



Chsetoceros sequatorialis Cl. 



This species has several small chromatophores, which pass into the awns. It thus 

 belongs to Gkan's group Fhceoceros. Also C. rostratus Laudek belongs to the same section. 



Chsetoceros Aurivillii Cl. n. sp. 



(Pl. VIII, tig. 10). 



Chains rigid, composed of elongated cylindrical cellules. Foramina smail, rounded 

 hexagonal. Celkdes three times longer than broad, convex and silicious. Valves Ijvoadly 

 oval, as long as the zone. Awns very long and stiff, arising at some distance from the 

 margin, firmely united at their bases, with spirally arranged small spines. Of the awns 

 two are shorter and nearly straight, two longer and curved in the same direction as the 

 former. Cell-contents with numerous chromatophoi'es, which pass into the awns. Length 

 of the pervalval axis 0, 045 mm., of the sagittal 0, 015 and of the transverse 0,oii mm. 

 Awns attain a length of 0,2 mm. 



I found this species is a sample, collected in January 1898 north of S. America 

 (7° N. 53° W.), låter in samples from the Malay Archipelago. It seems to be a very rare 

 tropical species. 



Clisetoceros calvus Cl. n. sp. 



'■"'"'•'• ' ■■' '■'' (Pl. VIII, fig. 11). 



Chains long, twisted, of closely connected, slightly silicious cellules. No foramina. 

 Cellules short, the sagittal axis being 3 times longer than the pervalval axis. The trans- 

 verse axis half as long as the sagittal axis. The narrower sides of the valves are convex, 

 80 there is a small sinus between two cellules, and the awns arise from the interiör of 

 these sinuses. The awns are very faint and easily löst, joined to two cellules by a fine 

 thread (as in C. anastomosans). The cell-contents with numerous, rounded, not very 

 small chromatophores. Length of the longitudinal axis 0, 01, of the sagittal 0,03, of the 

 transverse 0,ui4 mm. 



'" ' ' • Chsetoceros coarctatus Lauder. 



This is a very common tropical species, which occurs both in the Indian and the 

 Atlantic Oceans- The awns are somewhat dissimilar in the same chain, and one may 



