SPECIES OF DESMIDS. 99 



aa. Cell J^ or less longer than broad (pV). 



bb. Semi-cells urn-shaped; diameter -j-J-j- in. (50/i) . urnaforme, loo 



bb. " more or less quadrate; basal lobes horizontal, emargin- 



ate; protuberances minutely granulate . . . gemmatum, loi 



bb. Semi-cells more or less pyramidal, basal lobes emarginate, 



insular e, 104 



ic. Angles of end lobe acute . . elegans, io6 



cc. " " rounded or obtuse (dd). 



dd. Diameter -^ to ^^ in (32-38/^) inerme, 104 



dd. " TsW'"- (14/^); length -5-I-5- (28/Y) . crassicolh, 105 



dd. " yJj-5- to y^ in. {20-22 jS); length ^ (28/*), 



compactum, 107 



iff. Angles of end lobe acute (# ). 



f(f. " " obtuse or rounded {gg). 



ff. End notch broad, gaping, the apices upright . . . binale, 107 



ff. " narrow, close, the apices horizontal . . simplex, 106 



gg. End broadly rounded, continuous with the sides; diameter -j-^jj^ 



(14//), .... obtusum, 107 



gg. " " " " " " semi-cells wedge- 

 shaped; diam. 24-28/^ . . ameatum.** 



gg. End elevated above the sides, a small projection near the apex on 

 €ach side .... . . cornpactum, 107 



gg. End elevated, no lateral projections . . . pingue, 105 



22. MICRASTERIAS. FIG. 22. FIVE FORMS. 



§ Cell more or less circular (i). 



§ Cell oblong (2). 



I. End lobe narrow, lengthened into divergent arms {a). 



I. " " not lengthened into arms, semi-cells 5-lobed [b)^ 



1. End lobe broad, not lengthened mto arms [c). 



2. Semi-cell 5-lobed, lobes horizontal; end lobe with 4 arms (d). 

 2. " " " " end lobe with 2 arms (z). 



2. " " lobes not horizontal, approximate; no arms (aa).. 



2. Semi-cell 3-lobed, lobes horizontal; end lobe with 4 arms (d). 

 2. " " " " end lobe without arms (/). 



a. Semi-cell 5-lobed {k). 



a. " 3-lobed, lobes radiate (/). 



b. End lobe not or slightly exserted (/). 



b. " conspicuously exserted (r). 



