The Botany of Iceland - 01.12.1928, Side 69

THE AERIAL ALGÆ OE ICELAND
393
This form may be described as follows: Valves lanceolate, with
obtuse apices, somewhat gibbous in the rniddle. L. 37 /t, br. 11 /r, str.
18 in 10 fi, puncta 14 in 10 fi. Raphe soinewhat shortened at apices;
apical area narrow, at each of the apices expanded to a
round area, in the middle to a square transapical area with
an isolated point on one side. In the girdle view the cell
is seen to have convex faces. It is probably the same form
as is described by Playfair (1. c.), even though there are
certain deviations. Thus one figure sliows a specimen desti-
tute of transapical area, while the raphe is shown reacliing
to the very apices of the valve. However, the description and
tigures are altogether somewhat incomplete, amongst other
things information as to the striation of the valves is entirely
lacking.
A form very much resembling the one here described is
mentioned and figured by Zimmermann (1919, p. 99, Pl. III,
fig. 4. Naviculci mutica v. rhombica). It diífers from this spe- Fig. 18
cies, however, by its undulate side walls and finer striation, Navicula
as also by being smaller. Bristol (1920 p. 69, íig. 9,1) has '^"j-hombot-
likewise a figure of a form of Navicula mutica bearing great gea piayfair.
resemblance to the present form. Finally Hustedt mentions (x 1200).
a similar form (1921, p. 153, Taf. I, figs. 13—15), opining
that it is identical with N. Lagerheimii Cl. (1894, p. 101, Pl.VII, fig. 11).
I doubt the correctness of this identification, however, and I have tried
to procure original material from the Riksmuseum at Stockholm where
Cleve’s collections are preserved. This was not possible, however, since
the collection has not yet been arranged. One of Hustedt’s figures
corresponds closely to N. mutica var. rhombica Zimmerm. in appearance,
the other two agree with the form here described which I must provi-
sionally regard as a separate forma that cannot be identified with
N. Lagerheimii until Cleve’s original preparations or material of this species
have been examined. The same form will be found in Van Heurck’s
Types No. 114 together with a typical N. mutica var. Göppertiana corre-
sjionding to Van Heurck Syn. Tab. 10, íig. 18b.
That the form mentioned here, like the other forms of Navicuta
mutica, is of pronounced aerial occurrence is beyond doubt, and since
it occurs in company with f. Cohnii in all 3 samples, it probably requires
the same life conditions as the latter in order to thrive well.
— — f. Wulffii Boye P. Boye Petersen 1924 II, p. 312, fig. 2.
N. Icel. L. 182, 241.
This form is characterised by its perfectly symmetrical valves which
are oblong, slighlly rostrate, with broadly rounded apices. L. 17—27,«,
br. 6—8 p, str. in the middle 14—18 in 10/t, closer towards the apices,
abt. 24 in 10 /t.
Area: Only known from Greenland.
Navicula nitrophila Boye P. n. sp.
Valva ovalis vel lanceolata vel curte lineari, apicibus rotundatis vel