/ 



502 DE8CBIPTI0N OF \PolygastHca. 



oblong on one side with round ends, on the other with truncate ends. 

 Length 1 -600th. Length of frond one inch. 



ScaizoxEJiA. Grevillii. — Tufted, slender, capillary, branched, brown- 

 ish-green ; tubes dichotomous, transversely striated at the base ; 

 nariculae longitudinally and obliquely disposed, very large, with 

 longitudinal lines; oblong-truncate on one side; on the other, 

 lanceolate, acute; in length 1 -576th. Length of frond one and a 

 half inch. 



S. mucosum. — Particularly mucous and soft ; tubes (coelomata) 

 obsolete, contiguous, implicate ; naviculae very large, in rows ; on one 

 side, lanceolate-oblong, and obtuse at the ends; on the other, oblong 

 and broadly truncate ; in length 1.420th to 1 -360th. 



S. Ago/rdhii (Ehr.) = Micromega Bomhycinum (Kiitz.) — Lorica 

 (naviculae) very narrow, acute at both ends, placed in single series ; 

 tubes filiform, dilated in the position of the enclosed naviculae (See 

 fig. 208 which represents a bundle of these tubes magnified 300 

 diameters.) Length of naviculae l-720th. North Sea. 



S. itivestiens (Montague.) — Parasitic, fasciculate, minute, glossy, 

 opaque brown ; filament dilated at the base, and diffusely ramose ; 

 branches anastomosing ; naviculae in one or two rows (uni or biserial), 

 rather large ; each with two nuclei, and cymbiform. The two nuclei 

 of the naviculae are in shape of two isosceles triangles opposed base to 

 base. The naviculae are mostly in single series, very rarely in 

 double. Notes on the Cryptogamia of Guiana in Ann. des. Sciences. 

 Nat. vol. 14, 1850, p. 308. 



S. eximium. (Thwaites.) — ThaUus simple or sparingly branched, 

 rugose; naviculae sigmoid, smooth, (Ann. Nat. Hist. 1848, p. 169.) 



The sigmoid frustules of this beautiful fresh- water species at once 

 distinguish it from any other described Schizonema. The delicate 

 gelatinous sheaths are simple, or very sparingly branched and 

 minutely rugiilose, especially near the base ; they contain from one 

 to four rows of the large, smooth, sigmoid finistules. Found in the 

 filaments of Vaucheria, stems of grasses, &c. In a stream near Bristol. 



S. subchcerens (Thwaites.) — The tubules (sheaths) cohering in an 

 amorphous mass, very numerous, branched ; containing oftentimes 

 many single rows of naviculae ; naviculae broadly truncate, suddenly 



