Naviculacea .'] infusorial ANiMAtcutEs. 487 



whether they are sufficiently distinct, as I find that the form of the 

 frustules varies even in the same specimen." 



'E^CYO^-Eyih. paradoxum (Kutz.) = Gloeonema paradoxum (Ehr.) — 

 Tnhules scattered, solitary ; frustules on secondary side acuminate, 

 homed, and striated. Length of frustule 1 -660th. Parasitic on 

 Conferva, Germany, Italy, Falaise, &c. 



E. prostraiian = Schizonema prostratum (Gi-ev.) — Forms a gelati- 

 nous sti-atum; tubules 'very much interwoven; frustules smaller, 

 rather obtuse, not horned, striated. Length of frustule l-996th. 

 Itah^, England, &c. (P. 17, f. 22.) 



(Ralf's Loc. Cit.) The tufts, when recent, are dark brown, but of 

 a dull green colour when diied. It is soft, but not gelatinous, 

 adhering only imperfectly to paper or glass. 



The filaments are short, straight, or flexuose, simple, or slightly 

 branched, slender, subequal ; quite coloui'less under the microscope. 

 Generally, the frustules fomi a single series, and have their convex 

 margin alternately in opposite direction. 



Genus Ertjstttlia. — Characterized by a double envelope, the loricse 

 being enveloped, and either scattered or grouped together in an 

 amorphous gelatinous mantle, or lacerna. The true lorica has six 

 openings, two at each end, and two in the middle. The ova cluster 

 is divided into from two to four leaf-like portions ; digestive cells 

 and bright glandular organs are often visible. This genus is closely 

 allied to Navicula. No figure is given in Die Infusionsthierclien. 



It is admitted by Kiitzing, in his family Navicidea;, under the section 

 ScMzonemece ; but Frustidia appendiculata is excluded. 



F. appendiculata. — Lorica (navicular bodies) straight, lanceolate, 

 and smooth (?) with obtuse ends, scattered in the gelatinous envelope. 

 Lorica like that of Navimla gracilis, but rounded on the dorsal and 

 ventral surfaces, and more parallel on the lateral ones. The central 

 opening is broad transversely, terminal foramina round, self-division 

 often observed. Mineral springs of Cai-lsbad. Length 1 -800th to 

 l-1150th. 



F. maritima. — Smooth (?) ; ends rounded, combining in groups, in 

 contiguous, but distinct, gelatinous cells. Length 1- 1200th to 

 1-11 50th. Alive in sea- water. 

 This species occiu's as a brownish jelly-like mass on stones, and 



