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



Very minute, brown; frustures cuneate, curved, often nearly ses- 

 sile j sometimes, especially in the maritime variety, on an elongated 

 branched stipes, generally binate, though occasionally as many 

 as four frustules are united together. Terminal puncta large ; 

 each of the puncta at the base, which are more evident than in 

 the other species, is connected with the upper punctum on the 

 same side by a line passing down the frustule. A slight notch 

 or punctum is present at the centre of the concave but not of the 

 convex margin; lateral surfaces very narrow, generally clavate, 

 striated. 



This species differs from all the foregoing in its curved frus- 

 tules, in having a notch on one only of the lateral margins, and 

 two strise passing down the frustule and connecting the upper 

 and lower puncta. 



I have attempted in vain to find some specific character to di- 

 stinguish the maritime form. It is more branched, has a very 

 rigid appearance, looking indeed not unlike a zoophyte, and the 

 striae connecting the puncta on the front surface are strongly 

 marked ; but intermediate specimens are occasionally met with 

 in which all these differences vanish. 



Plate XVIII. fig. 9. Gomphonema minutissimum. 



8. G. paradoxum, Ag. Frustules broadly cuneate, puncta at the 



upper end strongly marked, with a stria from each passing down 



the frustule ; lateral surfaces clavate, narrow, not striated. Ag. 



Consp. Diatom, p. 34 ; Harv. Br. Alg. p. 208 ; Kutz. Syn. Diatom. 



p. 569. Echinellaparadoxa, Grev. Crypt. Fl. t. 25 ; Eh. Die Infus. 



p. 221 ; Pritch. Infus. p. 208. 



On marine algae very common. 



This species forms a brown gelatinous covering on the smaller 

 algae ; it turns green in drying. At first the frustules are nearly 

 sessile, but when mature they are attached to a more or less 

 branched stipes forming a fringe on the infected plant, which is 

 distinctly visible to the naked eye ; the frustules are broadly cu- 

 neate, vidth two conspicuous puncta at the upper end, and two 

 strise extend the entire length of the frustule. There are no 

 puncta on the lateral margins ; the lateral surfaces are very nar- 

 row in comparison with the front, much more so in fact than in 

 any of the preceding species ; they are clavate in form and not 

 striated. 



I am not sufficiently acquainted with Gomph. majusculum, 

 Harv., to make any remarks upon it. 



Plate XVllI. fig. 10. Gomphonema paradoxum. 



Analysis. 



{Lateral surfaces of the frustules constricted beneath the 

 apex so as to appear urn-shaped 2 

 Lateral surfaces not urn-shaped 4 



