70 Bristol . — ( 9 /z the Alga- Flora of some Desiccated 
sides; the number of undulations varied in different individuals, being 
either two (Text-fig. 9 , 26) or three (Text-fig. 9 , 27 and 28). The striations 
were usually 22 to 24 in 10 /x, rarely about 19. In all other respects this diatom 
agreed with the above species, but the general configuration of the valves 
was so characteristic that it seemed best to regard it as a special variety, 
under the name undulata. 
10. Navicula exilissima , Grun. (Text-fig. 9 , 22-23). 
The markings on this minute diatom, found in two soils, were very 
difficult to see, but there were about 41 or 42 striations in 10 /x. The valves 
were 10 to ii/x long by about 3*5 /x broad, and elliptical in shape with 
somewhat pointed rounded ends. The striations were interrupted in the 
middle, producing a false stauros, and did not quite extend to the raphe. 
The species has not previously been recorded for this country. 
11. Navicula Atomus , Naeg. (Text-fig. 9 , 9-13). 
The extremely characteristic form of the raphe in this species made 
its identification comparatively easy. It was found in sixteen different soil- 
samples, though this is the first record of its existence in the British Isles, 
and was oval in shape, usually 9 to 1 1 ju. long by 4*5 /x broad, and extremely 
delicate. The raphe was surrounded by a clear hyaline zone which did not 
expand opposite the median nodule to form a false stauros ; the striations, 
about 26 to 30, frequently 28, in 10 /x, radiated out from the central nodule. 
This is a considerably larger form of the species than that described by 
Van Heurck. 
12. Navicula contenta , Grun., var. biceps , Del. (Text-fig. 9 , 14-17). 
This species has not previously been recorded from the British Isles, 
yet fourteen different soil-samples yielded the variety biceps , usually in 
considerable quantity. The markings were difficult to make out, but the 
very characteristic form of the valves, which were united into long chains, 
left no doubt as to their identity. The valves were 9 to 12 /xlong and 
3 to 3*5 M broad ; while the swelling opposite the median nodule was either 
absent or feebly developed. There appeared to be about 38 striations in 
10 /x, with a gap in the middle producing a false stauros, but in the majority 
of cases it was impossible to see this. The siliceous wall was very thick in 
comparison with other diatoms of the same size. 
13. Hanizschia amphioxys , (Ehr.) Grun. (Text-fig. 10 , 1 and 2). 
The forms of this ubiquitous species which occurred in the cultures 
were usually small, about 30 to 40^ in length by 6*5 to 7 /x in breadth, but 
occasionally larger forms were observed, even up to 60 /x in length. In the 
larger form (Text-fig. 10 , 1) there were 7 carinal points in 10 /x and about 16 to 
17 striations, but in the smaller forms the carinal points were more numerous, 
frequently 8 to 9 and sometimes even 10 in 10 /x, while there were about 20 
striations in 10 /x. In each case the two median carinal points were some- 
what widely separated and a rudimentary nodule could be seen between 
them. 
