4: A. DE BREBISSON ON SOME FRENCH DIATOMACE^. 



different from my S. crumena ; thence came the observation I ad- 

 dressed to W. Smith, which determined him to announce in a note 

 to his 2nd vol., -p. 89, that I had recognised characteristic differ- 

 ences between S. crumena and S. Brightwellii. Since then I have 

 had numerous specimens from England, from W. Smith himself, 

 from W. Arnott, and M. G. Norman, which have convinced me 

 that it was one and the same species. Only it is possible that TV. 

 Smith's figure, quoted above, ought to be referred to a form with 

 large and rounded valves of S. subsalsa. This latter species is 

 especially distinguished by its inferior summit of the valves, which 

 is attenuated and considerably hollowed into a gutter, and by the 

 presence of applied wings, but these are raised and more apparent 

 near the summits. The valves are also generally oval, while in the 

 crumena they are nearly always circular, and so much so that 

 Kiitzing in his Spec. Alg., p. 19, thought proper to unite this 

 species to his Cyclotella Meneghiniana as variety p. major ; a con- 

 nection which it is difficult to understand, if we remark the double 

 direction of the canaliculi which converge towards two diametrically 

 opposite points of the circumference, the two summits (Poli Rab.) 

 instead of radiating regularly in the direction of one centre, as is 

 the case in the Cyclotella. 



Surirella minuta Breb. (in Kiitz. Spec. Alg.) although this 

 Diatom is always smaller than the ovata, that its colour is darker, 

 more blackish, and that its figure is different, it is very probable 

 that it is only a form of S. ovata to which ought to be united also 

 a certain number of pretended species which are common in 

 brackish waters. 



Nitzschia Brebissonii W '. Sm. syn..i., p. 38 (exclus. synonym). 

 I had no right to the honour of this dedication, which must be 

 accepted in order to avoid rendering the synonymy inextricable. 

 This species, from brackish waters, differs completely from Sigmatella 

 Brebissonii of Kiitzing, which inhabits fresh water, and is only a 

 broad and but slightly sinuous variety of Nitz. sigmoidea y a variety 

 which may be called Armoricana in order to avoid a source of 

 errors. It was the Synedra Armoricana of Kiitzing (Bacill, tab. 4, 

 f. 34.) 



Nitzschia obtusa W. Sin. (syn. i., p. 35, pi. xiii, 107.) Pools 

 of brackish water near Trouville This species is found in abundance 

 in the midst of the filaments of alga which carpet the surface of 

 the pools. If was thought that the filaments had originally con- 



