488 On Diatoms fron Chincha Ouano. 



37. Coscinodiscus perforatus, var. cellulosa, A. S. Rare. 



38. Coscinodiscus polyacanthus, Giun. Not rare. 

 Resembles C. suhtiUs, but has numerous marginal spines. 



'MJ. Coscinodiscus subconcavus, Grun. Not very rare. 



40. Coscinodiscus subtilis (Elir. ?), Grun. Rare. 

 Without marginal spines. 



41. Spermatogonia antiqua, Leud. & Fortmorel. (PI. XVI. 

 figs. 16-21.) Not rare. 



This curious form, as to the nature of which there still exist 

 some doubts, was originally found in Java ; but it seems to be 

 a widely distributed species. Besides the Chincha guano, I 

 have observed it In New Guinea (Tami Islands) and very 

 often among diatoms from the Adriatic Sea (Triest), and 

 Cleve has recently found it in the Plankton of the Atlantic 

 Ocean *. 



The inflation at the lower end is not triangular, as described 

 by Leudiger and Fortmorel, but has exactly the form of the 

 head of a human spermatozoon. The frustule is usually not 

 straight, but more or less sigmoldally bent. The upper part 

 is enlarged and terminates in a point ; one margin of the 

 enlarged portion is more straight, the other is always convex, 

 sometimes angular (fig. 17). The striai are not capitate, as 

 described by the authors, tliis appearance being due to the 

 fact of their crossing the double outlines of the frustule. It 

 might be that the strise are superficial ribs, which give to the 

 margins a somewhat indented appearance of the same kind 

 as in Thalassiothrioc, although in a much lesser degree. The 

 number of striae is 8 in 001 mm. ; they gradually disappear 

 near the lower end. Figure 21 represents a small and 

 straight individual with an obscure longitudinal line which 

 might possibly be a kind of keel. 



Length: 0096 O'llS _0a26 OOo^ 0-1(31 X 

 Breadth : 0003 00024 0035 0004 0-004 O'OOS* 



The Chincha guano contains also a form known as Acti- 

 m'scus sirius, Ehr., which, however, is not a diatom, but 



* Cleve, ' A Treatise ou the I'hjtoplankton of the Atlantic and its 

 Tributaries' (Upsala, 1897), p. 25. 



