484 DESCEiPTioN OF \^Polygasirica, 



stipes short, bacilli exactly linear, with trimcate ends : margin very 

 smooth, dorsally very narrow, dilated at the ends into obovatc small 

 heads. Length l-48th. Coast of Dalmatia. This differs much 

 from the species so named by Ehrenberg. 



Stnedka rumpens. — Attached in a tabulate manner, tables at 

 length breaking up ; wands very narrowly Knear, rather tumid, and 

 obtuse at the ends; cohering by alternate angles. In brackish 

 water. German coast. 



Sub-section III. Laceenat^. Compound Navicul<z. — 



The individual siliceous frustules, or lorige, are themselves included 

 in a gelatinous mass ; hence Ehrenberg views them as having a double 

 lorica, or as compound forms, in contra-distinction to the rest of the 

 Naviculacea, which are in his nomenclature called simple. 



Genus Berkeleya (Grev.) — " Frustules linear, included within 

 tubular, sub-membranaceous filaments, which are free at one extre- 

 mity, but have the other immersed in gelatinous tubercle." (Ralfs, 

 Ann. Nat. Hist. v. 16, p. 110.) 



" This genus differs from Homoeocladia and Schizonema, in having 

 the base of the filaments immersed in a tubercle." It belongs to 

 Kiitzing's family, Naviculece, sect. Schizonemece. 



B. fragilis. — Filaments hyaline, sub-simple, minute; frustules 

 niimerous, crowded, lanceolate, or linear-lanceolate, eight to twelve 

 times as long as broad, ends truncate, in length 1 -360th., not 

 striated. 



" When recent, the plant is dark olive-brown with a slight lustre ; 

 when dried is greener, and generally glossy. Filaments very short, 

 seldom exceeding a quarter of an inch in length, and pale at their 

 immersed base, from which they issue in a radiate manner ; usually 

 simple, but occasionally dichotomous. The tubercle is colourless, 

 gelatinous, large in proportion to the size of the plant. Parasitic 

 on Zostera rnarina, and smaller sea Algae. British Coasts." 



B. Adriatica (Kiitz.) — More loosely branched; the branches with 

 distinct subdivisions ; frustules narrowly linear-lanceolate, and 

 rather obtuse. Length 1 -300th. Trieste, Adriatic Sea. (P. 17, 

 f. 34, 35, a. h.) 



Genus DrcKiEiA (Ralfs.) — Frond sub-gelatinous, tender, plane, 

 attenuated toward the base, undulated ; containing oblong fmstules, 



