CYMBELLA.. 427 



Cocconema cistula Ehr., Die Infus. p. 224. pi. xix. f. 7. ; 

 Jenner, in Fl. of Tunbridge Wells. Cymbella copulata 

 Breb. and Godey. N. geminata ? Turp. (1828). 



Hob. Frequent in Sussex: Mr. Jenner. Cheshunt : A. H. H. 



The frustules in this species are shorter than in those pre- 

 viously described, more ventricose and obtuse. In C. lanceo- 

 latum the frustules are straight, in C. cymbiforme but slightly 

 curved, while in C. cistula they are considerably so. 



4. COCCONEMA VENTRICOSA? Hass. 

 Plate CI. Fig. 4. 



Char. Frustules small, straight, ventricose, obtuse. 



Cocconema? gibbum Ehr., Die Infus. p. 225. pi. xix. f. 9.; 

 Jenner, in Flora of Tunbridge Wells. Cymbella ven- 

 tricosa Ag. ? Flor. Bot. Zeit. ; Breb. and Godey. 



Hob. Cheshunt : A. H. H. Waterfall at Harrison rocks : 

 Mr. Jenner. 



This is the smallest species of the genus which has hitherto 

 been described. From Cocconema phcenicenteron, with which 

 it might be confounded, it differs in size and in the frustules 

 not being curved. 



78. CYMBELLA Hass. 



Char. Frustules cymbiform, striated, sulcated, not stipitate. 



Derivation. The diminutive of cymba, a boat ; in allusion 

 to the form of the frustules. 



This genus differs from Cocconema only in the frustules 

 not being stipitate as they are in that genus. Although not 

 stipitate, the frustules frequently are attached in the entire 

 length of their flat surface to other Alga, often to Clodo- 

 phora crispata. The Cymbella of Agardh embraces species 

 belonging to several distinct genera, and not one of those here 

 described under the name of Cymbella. The following are 



