146 THE AMERICAN MONTHLY [August, 



aa. Cell 3-3 times longer than broad ; diameter 3^ in. (75/j'-), 



hionerosu^n^ 99. 

 aa. Cell twice longer than broad; diameter ^^^^ in. (14//), Ltindellii. 

 aa. Cell \ or less longer than broad (<5(5). 



bb. Semi-cells urn-shaped ; diameter ^i^jj- in. ("^o//.) . . rirnaforme., 100. 

 bb. '' more or less quadrate; basal lobes horizontal, emarginate ; 



protuberances minutely granulate getnmatum., loi. 



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 -^-^ to ^^ in. (32-38//) iiterme, 104. 



dd. " y-g^^- in. (14//); length TT-jTT 'i"*- (28//) . . crassicolle., 105. 



dd. " TrV^tOy^W^ in. (20-22//) ; length t^i,, (28//), compactum., 107. 



ee. Angles of end lobe acute {jy). 

 ee. "• '• , 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 y^Vir (^4/')' 



obtustini^ 107. 

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



side compactii7n, 107. 



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



23. MiCRASTERIAS. 



§ Cell more or less circular (i). 



§ Cell oblong (2). 



I. End lobe narrow, lengthened into divergent arms («). 



I. " " not lengthened into arms, semi-cells 5-lobed (<5). 



1. End lobe broad, not lengthened into arms (c). 



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

 2. " " lobes not horizontal, approximate ; no arms, 



yenneri., 115. 

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

 2. " '' " '• end lobe without arms {y). 



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



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



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



b. " '^ conspicuously exserted (;-)• 



c. Semi-cells 5-lobed (w). 



c. Semi-cells 3 or obscurelv 5-lobed ; lateral sinus shallow, obtuse ; lateral 



angles mucronate decemdentata., 113 



d. Basal lobes with 3 linear processes on each side . . imiricata, 118 



d. " without linear processes, but (e). 



e. Forked once only, margins finelv serrate . Mahabideshzvarensis., 112 



e. " '' margins smooth Nordstedtiana., 113 



e. Forked twice (lobules forked) ; cytioderm spinous . . . spinosa.^ 



e. '' cytioderm smooth ; margins serrate . Hcr»iaiiuiana^ 112 



e. '• " '* margins not serrate, Americana^ ii3 



f. End lobe nearly as wide as the basal, apices deeply notched i^g) . 



f. " " " "• apices not deeply notched {Ji). 



*Journ. R. Micr. Soc, Dec, iS 



