Mr. J. Ralfs on the British species o/Eunotia. 459 



regret that I cannot detect any character to distingnish ' Frag, 

 aurea' from ' Frag, diatomoides,' except that the latter in di'ying 

 changes to a green colour. 



The following extracts from their letters will show that my 

 opinion has been confii'med by the observations of Mrs, Griffiths 

 and Mr. Harvey, who at my request compared these plants. 



Mrs. Griffiths wa-ites, " I have examined your specimens of 

 ' Fragilaria aurea' very carefidly, and compared them with * Fra- 

 gilaria diatomoides' from Torquay, gathered at different times, 

 and can find nothing to distinguish one from the other." 



]\Ir, Harvey observes, " I fear you are right about ' Frag, aurea ' 

 if colour be not in itself a specific character." 



Mr. Berkeley has enabled me to compare our plant \Aath the 

 ' Conferva striatula' of Jurgens' Algse, and thus to assure myself 

 that it is completely identical with Jurgens', which is doubtless 

 the ' G7-ammonema Jurgensii' of Agar dh. 



Plate XIV. fig.5 . Grammonema Jurgeiifsii : b, single frustule ; c, lateral 

 view. 



EuNOTiA, Ehr. 



Frustules free, simple or binate, quadrangular, with two pimcta 

 at each end ; the front is flat or concave, and the dorsum con- 

 vex ; the lateral surfaces are flat. 



Some species placed by Ehrenberg in this genus have cymbi- 

 form frustules and belong to Agardh's genus Cymbella, under 

 which they vnW. be described. 



In Eimotia the frustules resemble those of some species of Fra- 

 gilaria, from which the present genus differs only in not having 

 its frustules imited into a filament. 



Viewed laterally the fi-ustules are kmate. The lateral surfaces 

 are flat, and do not enter into the front ^^ew, which is quadi'an- 

 gular with two puncta at each end. Longitudinally the front is 

 flat or concave and the dorsum convex ; the convex surface is ge- 

 nerally raised in transverse ridges, and the number of these ridges, 

 as seen in a lateral \iew, when they appear like teeth, distin- 

 guishes the species. 



Professor Bailey suspects that "the number of these teeth is 

 liable to variation, and that the number of species has in conse- 

 quence been made too great*." 



1. Ell. inonodon (Ehr.?). Lateral view concave on one margin, 

 convex on the other and constricted near the ends ; striae none or 

 very obscure. Bailey, Amer. Bacil. in American Journal of Sci- 

 ence and Arts, vol. xlii. no. 1. pi. 2. f. 28. 

 In freshwater pools. Piltdown Common near Uckfield, Sussex, 



Mr. Jenner ; Penzance. 



* See American Journal of Science and Arts, vol. xlii. No. 1. 



3H3 



