English Soils: an Important Factor in Soil Biology . 67 
breadth from 4*5 to 6 /x. The costae are convergent towards the middle 
and divergent towards the apices, and are interrupted by a wide space 
opposite the central nodule; there are about 10 to 11 striations in 10 /x. 
The raphe is bent in the same direction on both sides of the central nodule 
and at the terminal Modules. 
5. Navicula elliptica^ Kuetz. 
(a) var. oblongella , Naeg. (Text-fig. 8 , 13). 
A form appeared in the cultures of one of the soils which agreed more 
nearly with this variety than with any other described form, and which 
certainly seemed to be very closely allied to it. The valves were oblong- 
elliptical, about 17 ju long and 6-5 \x broad, with an elongated hyaline area 
on both sides of the raphe swelling out into a conspicuous circular area 
around the median nodule, which was oval in shape. 
The striations were gradually radiating from the central nodule, about 
20 in 10 jx, and were interrupted near the raphe by a longitudinal furrow 
which was exactly parallel to the edge of the hyaline area. 
(b) var. minima , Van H. (Text- fig. 8 , 14). 
A small oval diatom, rarely more than 8 1 u. long, with a hyaline area 
and longitudinal furrow exactly similar to that of the above form, was 
found in two soils. The striations were radiating and about 17 to 18 in 10 /x. 
6 . Navicula terricola , n. sp. (Text- fig. 8 , 15-17). 
In one of the soils a diatom was found which resembled N. elliptica , 
var. oblongella , very closely, but which differed from it both in the more 
oblong form of the valve and in the character of the raphe. The length of 
the valve varied from 16-5 to 22 - 5 pt, and the breadth from 4*5 to 5 /x. The 
striations were slightly curved, almost perpendicular to the raphe near the 
median nodule and somewhat divergent towards the apices ; there were 
about 21 to 25 in 10 /x. The raphe was not straight, but the two halves were 
slightly sigmoid. The median nodule was oval and the terminal nodules 
circular. The raphe was surrounded by a conspicuous elongated hyaline 
area which was gradually dilated around the median nodule and towards 
the apices. The striations appeared to be interrupted near the raphe by 
a longitudinal furrow parallel to the edge of the hyaline area. No species 
has previously been described of which this diatom might be a form, hence 
it seems most satisfactory to regard it as a new species, nearly related to 
N. elliptica. The following is a diagnosis of the species : Valva lineari- 
elliptica, apicibus rotundis, media parte interdum nonnihil inflata. Rapha 
citra ultraque medium nodulum leviter sigmoidea, zona circumdata conspicua 
elongata hyalina circa nodulum atque apices versus dilatata. Striae leviter 
flexae, raphae media parte fere perpendiculares apices versus nonnihil diver- 
gentes, sulcis duobus ad zonae hyalinae margines parallele interruptae. 
Valvae 16-5 to 22-5 ju longae, 4-5 to 5 /x latae, striae 21 to 25 in 10 /x. 
Hab . in solo culto Harborne (Birmingham). 
