OF BRITISH FRESH-WATER DIATOMACE^. 5 



and Loch Etive, Argyllshire ; R. Calder and R. Avon, 

 Lanarkshire ; Lochleven. Fossil in the Mull earth and Glen- 

 shira sand. 



I have thus named the curious little form represented in 

 fig. 17. It is narrow, slightly arcuate, with rather square, 

 slightly expanding apices. On the generally concave side are 

 three rounded but gentle prominences ; the central one consi- 

 derable, the lateral ones, which are near the ends, very slight. 

 Strige conspicuous, sub-distant, about 20 in -001, not reaching, 

 or hardly reacliing, the median line, which seems to be, as in 

 the known CymhellcB, a little nearer the ventral surface. 

 There is in most cases a blank space round the central nodule. 

 Length from 0008 to 0012 inch. 



The characters of this species are very constant. It varies 

 somewhat in size, and a little also in the form of the apices, 

 which are in some less square than in others. 



I first noticed it in the Mull earth, then in a slide mounted by 

 Professor Smith for Gomphonema fiemmatum, the locality of 

 which was not given; then in the Glenshira sand, and subse- 

 quently in the other localities named. It has always been, 

 hitherto, scattered, and does not seem to have been yet found 

 in the spots where it grew. But it appears to be widely 

 diffused. 



18. Cijmbella turgida, W. G. Elgin. — This pretty spe- 

 cies has only occurred to me, as yet, in one British gathering, 

 from a moss near Elgin, but 1 have seen it in two speci- 

 mens of soil from South America. It is short and broad, 

 the dorsal line almost perfectly circular, while the ventral one 

 is nearly straight. The apices are acute, and somewhat pro- 

 duced. The two halves are very unequal, the dorsal being 

 very broad, the ventral remarkably narrow. Striae very con- 

 spicuous, strong and sharp, about 24 in '001. Length 002 to 

 •0025 of an inch. Of the British CymhellcB, C. maculata 

 comes nearest to it, but differs in form, in the shspe of the 

 apices, in striatum and in general aspect. In the Elgin gather- 

 ing the only one in which as yet it occurs, the species is very 

 uniform and well marked on its characters, 



19. Cymhella obiusa, W. G.— This species occurs in 

 many gatlierings ; as Lochleven, those from Banffshire from 

 Lanarkshire, Argyllshire, &c. Dr. Greville finds it in one 

 from Braid Hills. It is rather small, with very obtuse apices, 

 and the striae are inconspicuous, much finer than in any of the 

 known species. I think I have seen it named C. Scotica 

 but Professor Smith's figure of that species, which accurately 

 represents a very common form, is very narrow and has ex- 

 tremely acute apices. Length '001 to -0015. Striae about 



