COCCONEMA. 425 



Mr. Jenner. Cheshimt : A. H. H. Near Dublin : Prof, 

 G, J. Allman. Swansea : Mr. Ralfs. 



a 



This species differs from all the foregoing in its curved 

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

 and two striae passing down the frustule and connecting the 

 upper and lower puncta." — Ralfs. 



76. PODOSPHENIA. 



Char. Frustules ivedge-shaped, never constricted. Stipes none, 

 or very short. 



Derivation. From irovs, afoot, and a-^t^v, a wedge. 



This genus differs from Gomphonema in the absence of a 

 regular and branched stipes. In their young condition the 

 frustules are attached in the same manner as those of the 

 Exilarice. 



1. PODOSPHENIA? OCULATUM. 



Plate C. Fig. 9. 



Char. Frustules large, in front view wedge-shaped ; laterally 

 ovoid, striated. Strias short. 



Gomphonema oculatum Kiitzing, in Linn^ea, p. 568. f. 45. 

 G. rotundatum Ehr., xviii. f. 7. 



Hab. By the side of a rapid stream, parasitic on Lynghya 

 zonata, at Corham, near Bristol: Mr. Thivaites. 



A very beautifid species, for an examination of which in a 

 recent state I am indebted to Mr. Thwaites, its first and 

 only discoverer in this country. 



B. Frustules semi- elliptical. 



77. COCCONEMA. 



Char. Frustules stipitate, semi-elliptical, icitJi a longitudinal 

 furrow, striated. 



