140 



CYMBELLA. 



ll quadrata Breb. ! (A. quadi-ata Breb. in Kiitz. Alg., p. 94 ; H.V.H. 

 Atl., pi. 1, f. 24*), plate 1, fig. 2. 



Differs from the preceding by its subquadrangular form and its hyaline 

 condition, which renders details almost invisible. 



Marine. Same habitats as type-form. England (Norm.) ; Scotland (Greg.). 



The Amphora membranacea of W. Sm. (S.B.D., i., p. 20, pi. 2.,f. 29), 

 according to authentic specimens from his herbarium, in our opinion, is only 

 a narrow and oval form of A. ostrearia. The figure of W. Smith well repre- 

 sents its type-form. 



England ; various localities (Sussex, W. Sm. !) 



Amphoropsis Grun. in Syn. (1883). 



Auricula Castr. (1873). 



These two genera should be included in the Amphiprora and are described 

 subsequently. 



GENUS 2 CYMBELLA AG., 1830. 



Frustules free or stipitate, with valves more or less cymbiform, 

 divided into two unequal portions by the raphe and the central nodule 

 eccentric. 



Raphe generally more or less arcuate. Endochrome as in the 

 Amphora. 



The C/mbella are asymmetrical Navicula, presenting all 

 possible variations from the type form Navicula, from having 

 a lanceolate, straight valve to a valve in the form of an arc. 

 Authors have, from the genus Cymbella, created two different 

 genera, the genus Cymbella, properly so called, with frustules 

 free and the genus Cocconema, the frustules of which are 

 stipitate. All the Cymbella of our Section II. belong to the 

 old genus Cocconema Ehr. 



Cocconema having been described in 1829, and Cymbella 

 only dating from 1830, the earlier name ought to prevail, 

 but in order not to create confusion, we have preferred to 

 adopt the later, v.hich is now exclusively employed. 



We are not aware to what Syncyc/ia Ehr. iSjj, refers, in 

 which this author includes cymbelliform frustules arranged 

 in a ring, and of which one species S. Salfia, had been 

 observed at Wismar, in the Baltic Sea on some fucus. We 

 are much inclined to believe that this observation should 



Fig. 26. Cymbella . , ... : . 



Ehrenbergu Kiitz, be accepted with caution. 



