47G DEScniPTioN ov [PolygasMea, 



Striatetxa unipunctata (Ag. and Ralfs.) — Stipes slender, much longer 

 than the fiiistule, which has several longitudinal striae. Filaments 

 minute, pale yellowish-brown, consisting of but few frustules, which 

 cohere at the alternate angles; lateral surfaces lanceolate, without striae- 



S. tenimformis (Kalfs.) — Longitudinal series of transverse striae in 

 some specimens more or less evident on the central portion of the 

 frustules ; in others, the longitudinal striae, extending from the end 

 towards the middle, are serpentine ; stipes short. 



Var. [a.) — Frustules without transverse striae. Common. 



Tax, {h.) striata. — Frustules with longitudinal series of transverse 

 striae on each side, having a single curve near the base. Torquay. 



Var. (y.) serpentina. — Frustules with longitudinal series of trans- 

 verse stiiae ; the longitudinal striae on each side undulated ; also a 

 narrow longitudinal space without any markings. Torquay, Has- 

 tings. 



Genus Stnedua. — The yard or ell-measv/re Animalcules. — Are, when 

 young, attached by one extremity; at a later period, often free. 

 Lorica longer than broad, of the form of a wand (bacillus), prismatic, 

 destitute af a distinct foot or neck-like process, or at most it is rudi- 

 mentary; simple, (smooth or striated), with openings at the ends, 

 but none in the middle ; the cluster of ova (granular mass) is some- 

 times divided into from two to four leaf-like plates, or into purses or 

 lappets ; digestive cells have not been observed. 



This genus Kiitzing arranges in his Sii/rirella, and thus defines it- 

 Individuals bacillar, prismatic, rectangular ; ultimately attached by 

 one or other extremity ; secondary side equal to or less than the 

 primary, traversed by a very smooth median longitudinal line (no 

 central aperture). This last circumstance distinguishes Synedra from 

 Navicula. 



The number of known species being very considerable, Kiitzing 

 has distributed them in six sections, viz : 1 . Scaphularia, minute, 

 rarely attached and smooth forms. 2. Echinaria, smooth and finally 

 attached forms, mostly aggregated in a radiant manner. 3. TJlnaria, 

 attached, dividing in a flabelliform mode ; transversly striated, save 

 at the centre. 4. Tahdaria, affixed horizontally to a growing stipes 

 and dividing in a tabellate manner. 5. Grallatoria, with a long often 



