Diatoms from Chincha Guano. 485 



only in the greater relative length of the awns and the size, 

 which seems to be larger ; the surface of the endocysts is also 

 granulated. It might represent only a variety of C. incurvus. 

 I give here some measurements of the latter : — 



General length : 0023 0028 Q-Q29 0027 X 



Length of the valve : Q-Q14 Q'019 0019 00195 021 • 

 Breadth of the valve : X 0"010 0010 (MJ09 0WT5 



16. Chaetoceros Lorenzianus, Grun. Very common. 



17. Chaetoceros peruvianus, Brightw. Rare. 



There are a few moi - e species of this genus, which, however, 

 I was unable to determine. 



18. Khizosolenia styliformis, Brightw. Very common. 



19. Skeletonema costatum (Grev.), CI. Very common. 



20. Skeletonema costatum, var. spiralis, var. nov. (PI. XVI. 

 fig. 8.) Not rare. 



Differs from the type only in the oblique disposition of the 

 spines, which unite the frustules together ; the degree of in- 

 clination of the spines is variable, and there are always some 

 frustules in the same filament whose spines are straight, as in 

 the type species. 



Although Skeletonema costatum is known to me from very 

 different localities all over the world, I have never before 

 seen such a spiral disposition of the spines ; it seems therefore 

 advisable to regard the present form as a separate variety. 



21. Eucampia zodiacus, Ehr. Rather rare. 



22. Biddulphia (Triceratium) alternans, Bailey. Very 

 common. 



23. Biddulphia (Triceratium) alternans, var. variabilis, 

 Brightw. Rare. 



These two forms are generally regarded as belonging to 

 two distinct species — the second being characterized by the 

 irregular form of the valve, its concave margins and the acute 

 apices of the three ends ; the first having a regular form, 

 straight margins, and broadly rounded apices. The exam- 

 ination of both of these species from Chincha guano, in which 



