Mr. J. Ralfs on the British species 0/ Gomphonema. 463 



leaves of aquatic plants, is very minute, but still distinctly visible 

 to the naked eye. 



Stipes slender, branched ; frustules cuneate, varying in length, 

 the shorter ones most decidedly cuneate, the more elongated ones 

 often nearly linear, slender ; the terminal crest is much more de- 

 veloped in some frustules than in others, and but rarely nearly 

 obsolete ; the terminal puncta wanting or very minute ; lateral 

 surfaces transversely striated with a central longitudinal pellucid 

 line. In a young state of this plant the frustules are short and 

 the constriction below the apex is but slight ; in its mature state 

 this constriction is more evident, and the lateral surfaces are of a 

 narrow urn-shaped figure, often much attenuated at the base : the 

 end of the crest, appearing like a terminal point, adds greatly to 

 the beauty of this form. 



This species is easily distinguished from all except the follow- 

 ing by the terminal crest; from Gomph. cristatum it dififers in 

 being constricted below the apex and in its slender frustules. 

 Plate XVIII. fig. 5. Gomphonema minutum. 



** Lateral surfaces not constricted beneath the apex. 



4. G. cristatum. Frustules crested ; lateral surfaces striated, obo- 

 vate ; viewed laterally, the crest appears like a terminal point. 

 On Conferva glomerata in a stream near Shoreham, Kent, Mr. 



Jenner. 



Of this new and very distinct species I have only seen a soli- 

 tary specimen, found by Mr. Jenner in December last*. The 

 lateral view is very unlike that of any other species with which 

 I am acquainted. 



It is very minute ; the stipes slender, simple, or rarely once 

 divided ; frustules cuneate, somewhat rounded at the angles and 

 terminated by a crest ; the lateral surfaces are obovate, striated, 

 and the end of the crest appears like an apiculus. 



This species somewhat resembles Gomph. minutum on a front 

 view, having, like that species, a terminal crest, but it is a smaller 

 plant, the frustules are shorter and their angles rounded. The 

 lateral view also is broader, and wants the constriction which oc- 

 curs in Gomph. minutum below the apex. 

 Plate XVIII. fig. 6. Gomphonema cristatum. 



5. G. dichotomum, Kutz., forms a minute fringe on the leaves of 

 aquatic plants ; frustules linear-cuneate, terminal puncta very mi- 

 nute ; lateral surfaces lanceolate, faintly striated. Kutz. Synop. 

 Diatom, p. 569. f. 48. Gomph. gracile. Eh. Die Infus. p. 217. 1. 18. 

 f.3; Pritch. Infus. p. 227. 



This species forms a minute brownish mucous fringe on the 



* Mr. Jenner has since favoured me with specimens gathered hy him near 

 Farnham in Surrey, where the plant is more abundant than at Shoreham. 



