928 



STSTE3IAT1C HISTOET OF THE U^FUSOEIA. 



mine the genus, even before minute microscopic examination. We place 

 more reliance upon colour in the discrimination of species than some writers 

 allow. The colour for the most part depends upon the contents of the frus- 

 tules, and, according to our experience, is subject to little variation, except 

 in old specimens rendered unfit for comparison by the escape of the naviculae. 



pi. 69. f. 367. On mud in sheltered 

 places. Tufts of a duller brown than 

 S. Dillwynii, gradually turning in fresh 

 water to a dark olive-green, not quickly 

 becoming offensive. Frustules in form 

 and size similar to those of *S'. rutilans. 



S. cluhium (Harv.). — Eesembles S. 

 Dillwynii; but the long branches, naked 

 below, are furnished towards their sum- 

 mits wdth numerous cmied ramuU. Harv. 

 Manual, p. 212. = aS". Dillwynii /3, KA. 

 p. 101. Kocks, &c. Tufts unequal- 

 topped ; apices of ramuli acute ; naviculse 

 ver}^ minute and densely packed. 



S. virescens (Harv.). — Fronds very 

 slender, densely tufted, tenacious, very 

 much branched from the base; ramidi 

 numerous, curled, upper ones longest, 

 swelling towards the tips, which are 

 dark-coloured and end in a sudden 

 point ; naviculse minute. Harv. Manual, 

 p. 212. North Devon. Tufts dense, 

 brownish olive, not much altered in 

 drying. Under the microscope it has 

 much the appearance of S. Dilhvynii; 

 but the thickened, dark-coloured tips 

 are remarkable. 



S. rutilans (Trentepohl, Ag.). — Densely 

 tufted: filaments elongated, subsimple, 

 I browTiish and empty at base, hyaline 

 and filled with crowded linear-oblong 

 frustules at the apex ; when drv, shining 

 and reddish. Ag CD. p. 18 ; KB. p. 112, 

 pi. 23. f. 6. 1, 2. = Monnema rutilans, 

 Meneg. ^' It differs from S. Dilhvynii by 

 its more varnish-like lustre, reddish 

 colour when dry, and finer and more 

 simple filament" (Ag.), 



S. Hoffmannii (Ag.). — Filaments 

 tufted, subsimple, arachnoid, when dry 

 shining with a reddish lustre ; navicidas 

 small, smooth, crowded ; valves lanceo- 

 late, = S. rutilans, var, Hoffmatmi, KB. 

 pi. 23. f. 10; Monnema Hoffnianni, Meneg. 

 Europe, Aberdeen, (x. 207.) Professor 

 i Kiitzing makes this form a variety of 

 I S. rutilans ; but Meneghini observes that 

 i they differ in external characters and in 

 j the dimensions and shape of the navi- 

 cidfe. 1-1080" to 1-960". 



S. Balticum (E.), — Navicidas stiiated, 

 slender, linear-lanceolate, in front view 

 trmicate, in lateral view subacute, dense, 

 crowded in the intricately branched fila- 

 ments. E Inf. p, 236, pi. 20. f. \b.=S. 



* Central nodule transversely dilated. 



ScHizoNEMA cruciyer (S,). — Filaments 

 much di\dded ; naviculee crowded ; 

 valves lanceolate, acute, striated; me- 

 dian nodule transversely dilated into a 

 stauros. SD. ii. p. 74," pi. 66. f. 354. 

 Britain. Striae distinct, 40 in -OOl". 



2 * Central nodule punctiform, sometimes 

 obsolete. 



S. GrevilUi (Ag.). — Frond membra- 

 naceous, much branched, level-topped; 

 naviculae in front -view subquadrate ; 

 valves oblong-lanceolate, with 60 striae j 

 in -001". AgCD. p. 19; SD. ii. p. 77, ] 

 pi. 58. f. 364. = 3Ionnema GrevilUi, \ 

 Meneg. ; S. quadripunctatum, Harv. On j 

 rocks and mud. Fronds densely tufted, 

 bro^vTi, turning to a dirty verdigris-green j 

 when dried, and adhering imperfectly to : 

 paper. Naviculae large, crowded at base, | 

 m a single file near the extremities. S. 1 

 quadripunctatum of British ^\Titers is an 

 old state, and tm-ns of a rusty colom- in 

 drying. 1-576". 



S. crinoideum (HaiT.). — Filaments 

 very slender, achromatic, sparingly 

 branched, densely woven into a pale- 

 green or brownish stratum ; naviculae 

 very minute, disposed in an irregidar 

 loose series. Harv. Manual, p. 214. =*& 

 tenellum, KB. p. Ill, pi. 23. f. 8 ; Mon- 

 nema quadripunctatum, Meneg. Eiu'ope. 

 Filaments exceedingly slender, with long, 

 simple, flexuose branches. Brown when 

 recent, olive-green and glossy when dry, 

 1-1386". 



S. Dillwynii (Ag.). — Frond densely 

 tufted, rich brown, very slender; navi- 

 culae minute ; valves lanceolate-acute, 

 smooth, SD, ii. p. 77, pi. 58. f 366,= 

 Monema Dillwynii, GCF, pi, 297. Rocks, 

 mud, and Algae. Naviculae imper- 

 fectly silicious, more or less crowded, 

 especially near the extremities; fronds 

 turning deep green on immersion in 

 fresh water, and quickly acquiring an 

 offensive smell; generally glossy when 

 dried. 1-1000". 



S. imj^licatum (Harv.), — Frond capil- 

 lary, densely tufted, much branched, 

 curled, and " entangled ; naviculae very 

 minute, irregularly crowded ; valves lan- 

 ceolate, rather obtuse. SD. ii. p. 78, 



