FRESHWATER ALG. 49 
TABELLARIACE/E. 
Genus Denricuna Kiitz. 
76. DENTICULA TENUIS. 
Var, ANTARCTICA var. nov. 
(PI. IIL, figs. 156, 157.) 
Denticula temas Kiitz., Bacill. (1844), p. 43, t. 17, fig. virr.; Smith, Brit. Diatom., ti, (1856), p. 20, 
Pl. XXXIV., fig. 293. 
D. parva valvis late ellipticis apicibus rotundatis ; costis transversis validis, 
6-7 in 10p, in media parte rectis, sed polos versus gradatim plus minusve curvatis ; 
inter binas costas sunt due series punctarum subtilium, circa 6-7 in quaque serie in 
media parte valvarum ; polos versus punctze in quaque serie fiunt minus crebree, 
Long. valv. = 18-23; lat. valv. = 7-8 p. 
HTab.—Pond some distance behind hut, Cape Adare, January 9th, 1902; on ice, 
four feet above frozen watercourse through “ Penknife ice,’ McMurdo Bay, September 
13th, 1902. 
This was a relatively rare form, of which not many specimens were seen.* The 
new variety resembles var. frigida Grun. (= D. frigida Kiitz.) in some respects, 
but in the latter the number of coste is not as great as in var. antarctica, the coste 
are not curved near the poles of the valves, and there are more than two rows of 
dots between each pair of ribs. There is also resemblance to var. inflata Grun. 
(= D. inflata W. Smith), in which Smith (op. cit, Pl. XXXIV., fig. 294) figures 
many of the costee as curved (c/., however, Van Heurck, Synopsis Diat. Belg. (1880-85), 
Pl. XLIX., figs. 32, 33), but the curvature is different, as the convex surface faces 
towards the poles, whereas in var. antarctica it is the concave surface. 
In some of the valves the coste near the two ends were curved more towards one 
side than the other (fig. 156), leading to a certain degree of asymmetry. 
* The form here described bears an appreciable resemblance to the figure of Fragilaria antarctica Castracane, 
given by Castracane (‘ Chall.’ Rep., Diat. (1886), Pl. XXV., fig. 12); this figure shows the same characteristic 
paired rows of dots between each two ribs, and the general shape of the valve is also the same. The ribs are, 
however, much more delicate and are scarcely curved at the ends of the valves. Van Heurck’s figure (op. cit., 
1909, Pl. ITT., fig. 48) shows nothing of the punctulations. Some doubt may be felt as to whether the valve figured 
by Castracane really belongs to the genus Fragilaria. 
