464 DESCEIPTION OF [Polt/ffasirtca. 



and " living on aquatic j)lants in ponds and ditches, as a brownish 

 mucous fringe. By its terminal crest it resembles G. cristatum, but 

 is distinguished from that species by its slender frustulcs, and their 

 constriction below the apex." (Ralfs.) 



GoMpnoNEMA clavatum = G. sulrmnosum (Kiitz.) — Smooth, short, 

 and cuneiform ; stipes long, very slender, and not much branched. 

 Foimd living and fossil. Length l-720th. Cluster l-120th. 



G. rotunclatum. — Smooth (?), short, cxmeate ; obovate laterally ; 

 stipes long, subramose. Length 1 -240th. Li\dng and fossil. 



G. discolor. — Smooth (?), slightly excised at the wider, truncate 

 end. Length 1 -600th. Found in Siberia. Considered a doubtful 

 species by Kiitzing, 



G. olivacea = G. Berheleii (GreviUe andEalfs.) — Frustules broadly 

 cuneate or triangidar, striated ; lateral surface obovate, lanceolate ; 

 pedicle dense, mucose, short, and entangled, forming a gelatinous 

 pale brown mass. Length 1 -2300th to l-1020th. Common iu sti'eams 

 throughout Europe. 



The stipes is hyaline and more or less branched ; frustules minute, 

 short, triangular, easily detached ; puncta at the end strongly marked. 



" Var. I. (Ralfs.) — Scattered frustules more firmly attached to the 

 stipes, which can be detected without difficulty." 



G. eoronatum ( =G. capitatiim, of Etrui-ia.) — Laterally linear, 

 cuneate ; dorsum with four constrictions ; the anterior extremity 

 dilated and obcordate, the posterior pointed and lanceolate (P. 1 7, 

 f. 36.) Length l-480th. Fossil in the siliceous meal of San Fiore 

 and North America. 



G. Americanum. — Linear ; \T.ewed dorsally, presents three oblong 

 decreasing portions, produced by four constrictions, the anterior end 

 ovate, sub-acute. Length 1 -864th. Fossil in North America and 

 Iceland. 



G. Atigur. — Cuneate and linear laterally ; dorsaUy rhomboid, with 

 an acuminate base. Length 1- 960th. Among Confervas from Mexico ; 

 aUve and fossil also in England and France. The Mexican variety 

 has a mucro terminating the constricted apex. 



G. Anglicum. — With two dorsal constrictions ; anterior extremity 

 rounded, rather more slender than the oblong body, which tapers to 

 a linciU' apex. Is allied to G. suUilis. Irchmd and Mexico. 



