Naviculacea.] infusorial animalcules. 495 



but broken up into fibrous bundles (penicilli) at the apex ; rows of 

 naviculae lax, overlaycd by longitudinal flexuose, and interwoven 

 fibres. Length of frond half-inch. 



MicEOMEGA ehondroides. — Small, cartilaginous, olive-coloured; ter- 

 minal branches aggregate, clavate, obtuse, with scattered spiny hairs j 

 naviculse membranous, flaccid, minute. Length l-1380th to 

 1-1 320th. Length of frond one-sixth to one-third inch. 



M. spinescens. — Particularly spinous, rather dilated; terminal 

 branches acute, spiny ; rows and tubules very distinct, close ; navi- 

 culse lanceolate ; on the other side oblong, truncate. Length 1 -960th 

 to 1- 720th. Length of frond one-third to half-inch. 



M. albicans. — Setaceous, white, or oKve green; branches and branch- 

 lets equal in thickness, fasciculate or verticUlate ; naviculaa in distant 

 rows, lanceolate. Length l-1200th to l-1080th; tubules distinct. 

 Length of frond half- inch. 



M. poly dados. —^etnGeovi?,, dichotomously branched, branches long, 

 slender, rather rigid ; naviculae obsolete (membranous ?) flaccid, in 

 distinct tubules; spores elliptic. Length of frond 1 inch. 



M. pallidum. — Pale rigid, somewhat hard, much branched ; 

 branches and branchlets short, divergent, obtuse; naviculee in lax 

 rows, and in distinct tubules. Length 1 -720th to 1 -696th (P. 17, 

 f. 39, 40, 41, 42). 



M. corniculatum. — Stout at the base, rather firm, plane, dichoto- 

 mous, much branched at the summit, ultimate divisions spinous; 

 naviculee slender, lanceolate, in distinct tubules. Length 1 -600th. 

 Length of frond as much as two inches. Trieste. 



Var. (J.) — Ultimate divisions penicUlate ; fibrous. 



M. Blyttii. — Frond elongate, filiform, sub-divided many times in 

 a dichotomous irregular manner, cylindrical, not attenuate. On the 

 Russian coast. This is a doubtful species. 



Genus Nattnema (Ehr.) Monema (Greville). — Envelope double; 

 the inner one, or lorica, siliceous and navicula-shaped ; external one, 

 or mantle, gelatinous and tubular. From the self-division of the 

 lorica and body being perfect, whilst that of the mantle is imperfect, 

 they are developed in separated filifox'm tubes, often branched, and, 

 as a whole, presenting a conferva-like appearance. 



