FRESHWATER ALGLE. 53 



half-way between Black and Brown Islands, January 3rd, 1903 ; pond in ice off 

 Black Island, McMurdo Strait, December 31st, 1902. 



Next to N. 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, cf. for instance the figure of Messrs. West (op. cit., 

 PL XXVI. , 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 7o, 

 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. murrayl W. and G. S. West (op. cit., p. 285, 

 PL XXVI., fig. 130) comes very close to this form. 



The two forms may be described as follows : 



f. amphicephala (fig. 154). Valvis diametro 2^plo longioribus, iu media parte 

 valde inflatis, polis valde capitatis. Long. valv. = 22-25 /A ; lat. valv. in media 

 parte = 9 '5-10 fj.. 



f. elongata (fig. 155). Valvis diametro 3plo longioribus, in media parte inflatis, 

 apicibus subcapitatis vel plus minusve capitatis. Long. valv. = 35-38 /A ; lat. valv. in 

 media parte = 10-1 2 p. 



Fig. 155 represents a very extreme form off. elongata. 



Many of the specimens of N. globiceps showed the interruption by one or two 

 longitudinal lines of the strise, as described and figured by Messrs. West. In other 

 cases, however, I was unable to convince myself that this was the case, the striae 

 appearing uniformly punctate (figs. 154, 155). 



88. NAVICULA STAUROPTEROIDES sp. n. 

 (PL II., figs. 99, 100.) 



N. parva, valvis sublinearibus, diametro G-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 centralcm) brevioribus et radiatis, polos versus valde convergentibus 

 et gradatim abbreviatis. 



Long. valv. = 37-39 p. ; lat. valv. in media parte = 5-6 /A. 



Hal. 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 

 stria3, in the presence of short striae around the central area and in the absence of striae 

 at the extreme ends. It should also be compared with N. gibba (Ehrb.) Kiitz., which 

 is again a larger form ; it also differs in having more markedly capitate poles, in the 



