66 Bristol —On the Alga-Flora of some Desiccated 
nodule, however, but appeared to be quite straight. This form occurred in 
thirteen soil-samples. 
3. Navicula Brebissonii , Kuetz., var. diminuta (Text-fig. 8, 10-12). 
This diatom was also found in thirteen soil-samples. The valves 
were narrowly elliptical, about 19 to 24 /u long and 4-5 to 5 M broad, with 
10 to 11 costae in 10 pu The costae were mainly divergent and did not 
reach to the raphe ; they were interrupted opposite the median nodule by 
a wide space ; those nearer the middle were usually shorter than the rest. 
The raphe appeared to be quite straight. This form differed from the one 
originally described in that the central costae were not converging as a rule, 
but the agreement was so close in all other respects that it seems best to 
include it in the same variety. 
Text-fig. 8 . Soil-diatoms I. 1 and 2, Navicula borealis , Ehr, ; 3-5, N. Balfouriana, 
Grun. ; 6-9, N. intermedia , Lagerst. ; 10-12, N Brebissonii , Kuetz., var. diminuta , Van H. ; 
13, N. elliptica , Kuetz., var. oblongella , Naeg. ; 14, N. elliptic a, var. minima , Van H. ; 15-17? tV. 
terricola , n. sp. Figs. 1-14, x 1435; figs. 15-17, x 1715. 
4. Navicula intermedia , Lagerst. (Text-fig. 8, 6 - 9). 
Petersen has figured a diatom which he considers to be a form of 
this species (loc. cit., p. 293, Fig. 19) obtained from three Danish soils. A 
diatom almost exactly resembling Petersen’s form has appeared in the 
cultures of four soil-samples in the present work, and evidently belongs, to 
the same species, though no previous record has been made of its existence 
in this country. The valves are slightly constricted in the middle and have 
somewhat capitate apices; they vary in length from 17 to 27 ju, and in 
