Mr. J. Ralfs on the British species of Gomphonema. 459 



growing on Fragilaria virescens ; I have received from him both 

 dried and recent specimens ; in the latter I find the frustules so- 

 litary or binate, the circles being entirely broken up before the 

 specimens reached me ; but Mr. Jenner informs me that when 

 gathered they are united together so as nearly to form a circle. 

 As however they are not arranged on a plane as in Meridian cir- 

 culare, but stand nearly erect, somewhat like the staves of a tub, 

 which is broader above than below, when they dry and fall down 

 they necessarily separate, and gaps are produced in the circular 

 outline. In the dried specimens I find some of the frustules ar- 

 ranged in a circle, which however exhibits the gaps already no- 

 ticed, whilst others seem to be fasciculated. 



The front view cannot be distinguished from a frustule of Me- 

 ridion circulare, with which it agrees in size and form., and also in 

 having two conspicuous terminal puncta and a series along the 

 lateral margins. As in Meridian circulare, the lateral surfaces 

 have a few distant, strongly marked, transverse striae ; but they 

 differ from it most remarkably in the constriction below the apex. 



Plate XV 11 1, fig. 2. Meridion constrictum. 



Gomphonema, Ag. {Eh.) 



Frustules cuneate, solitary or geminate, terminating a simple or 



branched filiform stipes. 



The species with cymbiform frustules have very properly been 

 separated by Ehrenberg from Gomphonema, and now form his 

 genus Cocconema, the British species of which I intend to describe 

 in a future paper. 



The genus as thus restricted borders closely upon Styllaria and 

 Licmophora, and as it were forms a connecting link between them. 

 It is only in the young state that in a few instances its frustules 

 are sessile and resemble those of Styllaria, the frustules of which 

 however are always sessile; whilst in Gomphonema, although some- 

 times they are at first nearly or quite sessile, yet ultimately they 

 have an evident stipes, and in most specimens some frustules 

 may be observed thus elevated. Its connexion is still more inti- 

 mate with Licmophora, which indeed Kutzing unites with this 

 genus. Mr. Borrer suggests the propriety of making Licmophora 

 a section of Gomphonema. Mr. Berkeley observes, that " in Lic- 

 mophora the frustules again divide, which is the sole difference 

 between the two genera, as I many years ago pointed out to Dr. 

 Greville.^^ I am by no means sure that Kutzing is wrong in uni- 

 ting Licmophora with Gomphonema, but I have not ventured to 

 unite them, as the habit oi Licmophora is somewhat different. 



In Gomphonema the stipes is branched in a dichotomous man- 

 ner, and in all the species with which I am acquainted the frus- 



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