FRESHWATER ALG/E. 



53 



half- way between Black ami Brown Islands, January 3rd, 1903; pond in ice oil' 

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



Next to N. muticopsis and X. shackletuni 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 ("/' <"''> 

 PI. XXVI., fig. 135), Van Heurck's figure (./>. cit., Suppl. PL A, fig. 13), Wolle's figure 

 (Diatom, of North America (1890), PL IX., fig. 33), and JMigula's figure (<>]>. cit., PL 7u, 

 fig. 6). The one form is relatively short with a strongly bulged median portion 

 and prominently capitate extremities (fig. 15-1); 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 vur. I'li-ynitx of X. inurrai/l W. and G. 8. West (<>j>. cit., p. 285, 

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



The two forms may be described as follows : 



f. amphicepkala (tig. 154). Valvis diametro 2.]plo longioribus, in media parte 

 valde inHatis, polis valde capitatis. Long. valv. = 22-25 ^ ; hit. valv. in media 

 parte = 9'5-10/x. 



f. cloiti/nta (fig. 155). Valvis diametro 3plo longioribus, in media parte iiifiatis, 

 apicibus subcapitatis vel plus miuusve capitatis. Long. valv. = 35-38 fj. ; lat. valv. in 

 media parte = 10- 12 p.. 



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



Many of the specimens of N. <///</'<y/'x showed the interruption by one or two 

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

 cases, however, 1 was unable to convince myself that this was the case, the stria; 

 appearing uniformly punctate (figs. 154, 155). 



8tf. NAVIOULA STAUROPTEROIDES sp. u. 

 (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 eentrali magna elongato- 

 elliptica, platea axiali subangusta, striis levibus, 20-21 in 10 //., in parte mcdiana 

 (adversus plateam centralem) brevioribus et radiatis, polos versus valde convergentibus 

 et gradatim abbreviates. 



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



/A/A. On ice, .McMurdo Iky, September 13th, 1902. 



This species was rather rare. In general appearance it is much like a small 

 specimen of X. xt<iitri>/>/<-ni Gruu., from which, apart from its .--mailer size, it differs in 

 the non-curvature of the raphe at, the apices of the valves, in the closer placing of the 

 stria:, in the presence of short stria; around the central area and in the absence of stria: 

 at the extreme ends. It should also be compared with X. <jil>l>n (Ehrb.) Iviitz., which 

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







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