SPECIES OF DESMIDS. 99 



aa. Cell YZ or less longer than broad (bb). 



bb. Semi-cells urn-shaped; diameter -g-i-o- in. (5o/*) . urnaforme, TOO 



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



ate; protuberances minutely granulate . . . gemmatum, 101 



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



insulare, 104 



cc. Angles of end lobe acute . . elegans, 106 



cc. " " rounded or obtuse (dd). 



dd. Diameter ir J TF to -^ in (32-38^) ....... inerme, 104 



dd. " T^hr in. (i4/i); length v(r(2S/f) . . crassicolle, 105 



dd. " yrVg- to T -g4rr in. (20-22/1); length -y^. (28/1), 



compactum, 107 



ftf. Angles of end lobe acute (ff). 



ee. " " obtuse or rounded (&). 



/". 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 18 * 00 



(14/4), .... obtusum, 107 



gr. " " " " " semi-cells wedge- 

 shaped; diam. 24-28^ cuneatum.** 



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

 each side compactum, 107 



gg. End elevated, no lateral projections pingue, 105 



\ 



22. MICRASTER1AS. 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 into 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 (f). 



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



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



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



b. " conspicuously exserted (r). 



