286 W. AND G. S. WEST 



39 Navicula (Pinnularia) shackletoni sp. n. (PI. XXVI, Figs. 136-138) 



N. minuta, valvis anguste elliptico-lanceolatis cum polls valde productis levissime 

 subcapitatis et obtusis, platea central! minuta, platea axiali angustissima, striis 

 10-12 in 10 M, leviter radiatis, validis et non punctulatis, in medio striis duobus 

 utrobique adversus plateam centralem delicatissimis et valde indistinctis. Cellula 

 in aspectu cingulato anguste lineari-oblonga. 



Long. 25-29 p.; lat. 4-5 M. 



Hob. Clear Lake, abundant. 



This minute species should be compared with N. lanceolata Kiitz. var. tenella 

 (A. Schm.) Cleve [ = N. tenella A. Schmidt, Atlas Diat. 1876, t. 47, f. 45], from which 

 it is distinguished by its distinctly produced poles, its more distant and less radiate 

 striae, and by the two faint median striae on each side of the central area. 



N. cryptocephala Kiitz. is also a similar species, but the lateral margins of the 

 valves are more ventricose and the poles more distinctly demarcated from the elliptic 

 body of the valve than in N. shackletoni. Moreover, the striae are as a rule much 

 finer. 



In general outline N. shackletoni is not unlike N. El Kab forma lanceolata 

 0. Mil Her (in Hedwigia, xxxviii, 1899, p. 311, t. 12, f. 19), but the striation is much 

 coarser and differently disposed. 



Var. pellucida var. n. (PI. XXVI, Figs. 139-141) 



Var. platea centrali majori, leviter transverse dilatata, striis minus robustis, in 

 medio duobus utrobique brevioribus. Cellula in aspectu cingulato conspicue latiori. 



Long. 25-29 p.; lat. 4.5-4.8 M . 



Hob. In pond, Cape Eoyds, common. 



This appears to be a well-marked variety, but the distinctions are hardly such as 

 to warrant specific separation. The much greater width in the girdle view was a 

 constant and noteworthy feature. 



40 Navicula radiosa Kiitz. 



V. Heurck, Synops. Diat. Belg. p. 83, t. 7, f. 20. Pinnularia radiosa W. Sm. 

 Brit. Diat. p. 56, t. 18, f. 171. P. acuta W. Sm. 



Long. 74 ft; lat. 13 p.; striis 11-12 in 10 p.. 



Hob. Ponds on Mt. Erebus. 



The specimens were not altogether typical as the apices were as acute as those of 

 the var. tenella (Breb.) Cleve, Navic. Diat. II, 1895, p. 17, but the striations were 

 rather coarser than in that variety. 



