231 (U)NTR1BUTI0]S[S FROM THE NATIONAL HERBARIUM, 



Subfamily II. PENNATAE. Valvo not ('en Ually built; that is, not arranged in 

 relation toarentral point or focus, ]m\ rather to a median line; outline gener- 

 ally boat-shapod or rod-shnped, sometimes oval, ouneate, crescent-shaped, 

 or sigmoid; markings generally pinnate or transverse (imperfectly radiate in 

 some species of Canipyhuliscus); true raphe, or hyaline median line (pseud- 

 oraphe), or raphe obscured by hiieniX wings or keel (cryptoraphe) always 

 present; processes (horns, ppines, etc.) uncommon. 



A. Xo true raphe; a hyaline median line (pseudoraphe) present, rarely obscure. 



(FRAClLARIOrUEAE.) 



a. Frustules united to form a liblxm or zigzag chain; outline in zonal view 



rectilinear; zone gcmerally <'omposed of separate bands; valve long-oval 

 or lanceolate. (Tabellakieae.) 



a. Frustuh^ in zonal view unbent; valves not concave and convex. 

 (Tabellakunae,) 



Vahe transversely partitioned by internal vertical septa; that is, 



perp<Midi('ular to zone in zonal view Denlicula (p. 318). 



Valve not transverst^ly pai'iitif^ied (may he transversely undulate, 

 species of Grammatophora); internal septa parallel to zone in 



zonal view. 



Internal septa massive, generally undulate, approaching from 

 either end of the fmstule toward but not to the center, leaving 

 a nonseptate central space which appears in valval view as a 

 central oval in each valve; zone hyaline or longitudinally 



dotted Grammatophora (p. 319) 



Internal septa delicate, discontinuous, not undulate, inter- 

 rupted at thi-ee or more places, tlu' nonseptate spaces appear- 

 ing ill valval view as so many ovals along the valve; zone or 



zonal l)ands transversely marked Tessella (p. 321). 



h. Frustuh^ in zonal view bent; one valve concave, the other convex. 



(Entopyltnae.) 



Valve transverscdy ribbed^ the ribs on one side of the median line 



alternat ing with Ibose on the other side, the median line therefore 



zigzag; internal septa (m each side of the valve pierced with oval 



openings srt in a straigliL row parallel to and near margins of the 



val v(^. , - Entopyla (p. 323), 



Valve transversely libbed, the ribs on one side of the median line 

 continuous with those on the other side, the median line therefore 

 straight; inttTual septa on each side of the valve pierced with 

 oval op<'nings set in a zigzag row parallel to but distant from the 

 margins of the valve Gephyria (p. 324). 



b. IVustuh* solitary', ornni ted into a fan or forming a spiral band: not forming a 



ribbon or zigzag eliain; outline in Z(mal view rod-shaped or wedge- 



shap(*d; valve club-shaped. (Mkkidioxeae.) 



Zone composed of separatt^ bands; intt^rnal s(^pta pierced by a row of 

 large <tval (openings wliich in valval view give a steplad<ler appearance 

 to the i-lub-shaped valv<^ CUmacosphenia (p. 325). 



c. Frnslnles \niited to form a ribbon or zigzag chahi; zone not compused of 



sei>arate bands. (Fragilarieae.) 



a. Valve with transverse septa. (Diatomixae). . .riagiogramma{p, 325). 

 fc. Valve without transverse septa. {Fraoilariixae). 



Dimeregramma (p. 327). 

 B. Frustule having oiu^ \ alve with true raphe, the other with distinct or obscTire 

 liyaline me(li:ui line (pseudoraplie)- (Achnaxthoideae.) 



a. Frustuh^ in zotuiI view bent, (me valv(^ concave, the other convex; ouiline 



of valve long-oval or boat-shaj)ed. (AcHNANTHEAE).^c/ma7^^fee5 (p. 327). 



b. Frustule in zonal vi<^w straight; outlineof valve broad-oval or nearly round. 



(Cocconeideae) Cocconeis (p. 328). 



