68 Bristol . — On the Alga-Flora of some Desiccated 
7. Navicula (§ Diploneis) hyalina, Donk., var. minima, n. var. (Text-fig. 
9 , 18-21). 
An extremely minute diatom, which appeared, so far as it was possible 
to make out the details of its structure, to be a reduced form of N. hyalina , 
Donk., was found in two of the cultures. The valves were extremely 
delicate, about 11 to 13*5^ long by 3-5 to 4-5 fx broad, and so hyaline that 
it was extremely difficult to make out the details. The striations were 
extremely faint and could only be distinguished rarely and with difficulty ; 
they appeared to vary from about 27 to 37 in 10 /x. The raphe lay in a furrow 
which in Text-fig. 9 , 18 and 19, is shown to terminate abruptly near the me- 
dian nodule,' "and in Text-fig. 9 , 21, to be contracted at the apices. In certain 
individuals (Text-fig. 9 , 18 and 19) there appeared to be a double median 
nodule, but the frustules were so small that it is probable that this was merely 
a reduced form of the structure figured for N. hyalina , Donk., in Schmidt’s 
; Atlas ’, PI. 70 , Figs. 4 and 5 ; the terminal nodules were conspicuous. In all 
of the frustules there was visible a longitudinal furrow (?) running parallel to 
the margin of the valve about half-way between the margin and the raphe. 
It is quite possible that this minute form may be a new species, but 
the general resemblance in structure to N. hyalina , Donk., makes it more 
satisfactory to regard it as simply a minute variety of this species. 
8. Navicula mutica , Kuetz. (Text-fig. 9 , 1-7). 
This extremely variable diatom was observed in the cultures of 
seventeen different soil-samples, and appears to be one of the commonest 
soil-diatoms. A number of different forms were found, of which one (Text- 
fig. 9 , 5) appeared to be identical with that described by Grunow as 
N. Kotschyi ; this distinction seems, however, to be quite unnecessary since 
the characters of the diatom agreed extremely well with those of N. mutica . 
An interesting feature in this species was the great variation in the size of the 
puncta which made up the transverse striations. As shown in the figures, they 
were sometimes exceedingly small (Text-fig. 9 , 1 and 7), but they might be 
much larger so that only five or six were found in each striation (Text-fig. 9 , 
2-4). Sometimes the puncta appeared to be arranged in no definite order, but 
in other individuals they were arranged in more or less regular longitudinal 
rows on the valve (Text-fig. 9 , 3). In the great majority of frustules there were 
18 to 19 striations in 10 yu., but in Text-fig. 9 , 2 and 6, are shown individuals 
with only 14 to 16 striations in 10 y, the one in Text-fig. 9 , 6 , being still 
farther removed from the typical form by the oval shape of the valve. 
The breadth of the valve varied from 5 to 7*5 y and the length from 
about jo /x to nearly 30 y. 
var. quinquenodis , Del. (Text-fig. 9 , 8). 
This very characteristic variety of the species was found in four soils, 
and was observed to have the puncta arranged in very definite longitudinal 
rows so as to produce a regular pattern on the surface of the valve, as shown 
