COCCONEMA. 425 



Mr. Jcnner. Cbesbunt : A. H. 11. iS^eur Dublin : Prof. 

 G. J. Allman. Swansea : 3Ir. Ralfs. 



" Tbis species differs from all tbe foregoing in its curved 

 frustules, in baving a notcb on one only of tbe lateral margins 

 and two stria; passing down tbe frustule and connecting tbe 

 upper and lower puncta."-— Ralfs. 



76. PODOSPHENIA. 



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

 or very short. 



Derivation. From ttovs, afoot, and (K^t]!', a wedge. 



Tbis genus differs from Gomphonema in tbe absence of a 

 regular and brancbed stipes. In tbeir young condition tbe 

 frustules are attacbed in tbe same manner as those of tbe 

 Exilarias. 



1. PODOSrnENIA? OCULATUM. 



Plate C. Fig. 9. 



Char. Frustules large, m front view ivcdge-shajjed ; laterally 

 ovoid, striated. StriiB short. 



Gornphonema oculatum Kutzing, in Liuna3a, p. 568. f. 45. 



G. rotundatum Ebr., xviii. f. 7. 

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



zonata, at Corbam, near Bristol: Mr. Tkwaites. 



A very beautiful species, for an examination of wbicb in a 

 recent state I am indebted to INIr. Tbwaites, its first and 

 only discoverer in tbis country. 



B. Frustules semi- elliptical. 



77. COCCONEMA. 



Cdiar. Frustules stipitate, semi-elliptical, icith a longitudinal 

 furrow, striated. 



