Diatoms from Chincha Guano. 487 



31. Asteroinphalus malleus (or malleiformis), Wall., var. paci- 



fica, var. nov. (PI. XVI. figs. 11, 12.) Not very rare. 



Valve almost circular or slightly ovoid, with the upper 

 part (containing the median ray) a little narrowed. The 

 median ray is placed more or less asymmetrically, forming an 

 acute angle with the longitudinal axis ; its central part is 

 conical; 8 rows of puncta in 0*01 mm., the puncta bordering 

 the rays being a little larger than the others. 



Length : Q-Q4 3 0046 Q-Q51 Q-Q57 

 Breadth: 0-041 00455 0-050 0-057" 



This diatom greatly resembles the type species from the 

 Indian Ocean which has been described by Wallich, differing 

 from it in the central part of the median ray. In the type 

 species this central part is quadrangular, with a deep con- 

 striction in the middle, dividing it into two parts of equal size 

 and shape; in the var. pacifica this part has never such an 

 appearance, being of a more or less conical form. In order 

 to show more clearly this difference I have reproduced in the 

 fig. 13 the type species as given by Wallich. 



Although this difference is very constant, occurring in all 

 specimens which I have observed, and there is another differ- 

 ence consisting in the asymmetry of the median ray, still it 

 seems to me that these characteristics are too trifling to be 

 of any specific value. I think it therefore more reasonable 

 to consider the Pacific form simply a variety of the Indian 

 species. 



32. Asteromphalus variabilis, Grev. Very rare. 



Resembles exactly figure 7 of Greville, but has distinct 

 puncta, which are, I suppose, omitted in Greville's figures. 



33. Coscinodiscus radiatus, Ehr. Rare. 



34. Coscinodiscus radiatus, var. asteromphala, Ehr. Very 

 rare. 



The large central alveoles surrounding a small hyaline 

 circular spore are provided with elongated puncta along their 

 periphery. 



35. Coscinodiscus excentricus, Ehr. Very common. 



36. Coscinodiscus gigas, Ehr. Rather common. 



