488 On Diatoms from Chincha Guano. 



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



38. Coscinodiscus polyacanthus, Grun. Not rare. 

 Resembles G. subtilis, but has numerous marginal spines. 



39. Coscinodiscus subconcavus, Grun. Not very rare. 



40. Coscinodiscus subtilis (Ehr. ?), 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 sigmoidally 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 striaj are not capitate, as 

 described by the authors, this 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 Thalassiothrix, although in a much lesser degree. The 

 number of strise is 8 in O'Ol 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 0-118 Q'126 Q-152 Q-161 X 

 Breadth: 0003 00024 00035 0004 0-004 0005' 



The Chincha guano contains also a form known as Acti- 

 niscus sirius, Ehr., which, however, is not a diatom, but 



* Cleve, ' A Treatise on the Phytoplankton of the Atlantic and its 

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



