FRESHWATER ALGAAS. 53 
half-way between Black and Brown Islands, January 3rd, 1903; pond in ice off 
Black Island, McMurdo Strait, December 31st, 1902. 
Next to NV. muticopsis and N. shackletoni this was the most abundant Diatom. 
There are obviously two well-marked forms of this species; this the published figures 
of the species already show, ¢/. for instance the figure of Messrs. West (up. cit., 
Pl. XXVL, fig. 135), Van Heurck’s figure (op. cit., Suppl. Pl. A, fig. 13), Wolle’s figure 
(Diatom. of North America (1890), Pl. IX., fig. 33), and Migula’s figure (op. cit., Pl. 74, 
fig. 6). The one form is relatively short with a strongly bulged median portion 
and prominently capitate extremities (fig. 154); the other is longer, the median part 
is not so strongly inflated, and the capitate character of the apices is far less pronounced 
(fig. 155). The var. elegans of N. murrayi W. and G. 8. West (op. cit., p. 285, 
Pl. XXVL, fig. 130) comes very close to this form. 
The two forms may be described as follows :— 
f. amphicephala (fig. 154). Valvis diametro 25plo longioribus, in media parte 
valde inflatis, polis valde capitatis. Long. valv. = 22-25; lat. valv. in media 
parte = 9°5-10 p. 
f. elongata (fig. 155). Valvis diametro 3plo longioribus, in media parte inflatis, 
apicibus subcapitatis vel plus minusve capitatis. Long. valv. = 35-38 w; Jat. valv. in 
media parte = 10-12 p. 
Fig. 155 represents a very extreme form of f. e/ongatu. 
Many of the specimens of N. glohiceys showed the interruption by one or two 
longitudinal lines of the strize, as described and figured by Messrs. West. In other 
cases, however, I was unable to convince myself that this was the case, the stri 
appearing uniformly punctate (figs. 154, 155). 
88. NAVICULA STAUROPTEROIDES sp. 2. 
(BES igs: 99, 100;) 
N. parva, valvis sublinearibus, diametro 6-7plo longioribus, in media parte leniter 
et late tumidis, polis late rotundatis vel subcapitatis, area centrali magna elongato- 
elliptica, platea axiali subangusta, striis levibus, 20-21 in 10, in parte mediana 
(adversus plateam centralem) brevioribus et radiatis, polos versus valde convergentibus 
et gradatim abbreviatis. 
Long. valv. = 37-39»; lat. valv. in media parte = 5-6 p. 
Hab.—On ice, McMurdo Bay, September 13th, 1902. 
This species was rather rare. In general appearance it is much like a small 
specimen of N. stauroptera Grun., from which, apart from its smaller size, it differs in 
the non-curvature of the raphe at the apices of the valves, in the closer placing of the 
strie, in the presence of short strize around the central area and in the absence of strix 
at the extreme ends. It should also be compared with NV. gibba (Ehrb.) Kiitz., which 
is again a larger form; it also differs in having more markedly capitate poles, in the 
