FRESHWATER ALG.E 283 



Long. valv. 19 M; lat. 5.1 M. 



Hob. Lake on west side of McMurdo Sound. 



This minute Navicula was rather scarce amongst quantities of other diatoms, 

 especially Hantzschia elongata, Tropidoneis Icevissima, and Navicula muticopsis. 

 Careful examination of the valves with a one- twelfth- inch oil- immersion lens revealed 

 no trace of striations. Other examples of apparently smooth species of Navicula are 

 N. perlepida Grun., 2V. lineola Grun., and 2V. wwfo-P.antoesek. 



2V. glabemma should be compared with 2V. palpebralis var. minor (Greg.) V. Heurck 

 (Synops. Diat. Belg. t. 11, f. 11 ; = 2V. minor Greg.), from which it differs in being 

 smaller and more angular, and in having no striations. 



32 Navicula rhynchocephala Kiitz. forma 



Long. 51 M; lat. 10 n; striis 12 in 10 /j.. 



Hob. In pond, Cape Royds. 



The form noticed was apparently one of the intermediate states between the more 

 typical form (with subcapitate poles) and the var. amphiceros (Kiitz.) Cleve, Synops. 

 Navic. Diat. II, 1895, p. 15. The poles were slightly swollen and more obtuse than 

 the figure of var. amphiceros given by 0. Miiller in Engler's Bot. Jahrbuch. xlv, 1910, 

 t. 2, f. 20. The form was very similar in outline to " 2V. rhynchocephala var." in Cleve 

 et Grun. Beitr. Arctisch. Diat. 1880, t. 2, f. 33. 



33 Navicula muticopsis V. Heurck 



Diatomees, Result. Voyage du s.y. " Belgica," Anvers, 1909, p. 12, t. 2, f. 181. 



Long. 14.6-23 /*; lat. 8-9.1 /*; striis 13-14 in 10 M . (PL XXVI, Figs. 121-124) 



Hob. In ponds, and on the ground in the Penguin Rookery, Cape Royds. Also 

 in recent geological deposit containing diatoms. Clear Lake, Green Lake, Pony 

 Lake, and near Blue Lake. Lake on west side of McMurdo Sound. 



This was the most abundant of all the Antarctic diatoms collected by the 

 Expedition. It occurred in nearly all the ponds and lakes, often in quantity, but 

 was most abundant in the Penguin Rookery at Cape Royds. 



Considerable range of variation was exhibited by the valves, mostly in the character 

 of the poles, which were sometimes decidedly subcapitate, whereas at other times 

 they were merely " produced." The actual polar margin was frequently sub truncate, 

 but more often much more rounded. The central area was of variable form, from 

 a transverse stauros to a rounded area of considerable size. The striations in all 

 the specimens examined were 13 or 14 in 10 /*, and consisted of 3-5 puncta each, 

 except in the median part of the valve and at the poles. A solitary unilateral punctum 

 was present in the central area of some specimens, but no trace of it existed in others. 



In all cases the median portion of the valve possessed subparallel sides. 



The two following forms may be distinguished: 



Forma evoluta. Cellulse paullo elongate, infra polum unumquemque distincte 

 sed leviter constrictse ; striis 13-14 in 10 ^. 



