SPECIES OF DESMIDS. 91 



y. Central verrucse none or scattered on each semi-cell (z). 

 y. " more or less clustered on each semi-cell (aa). 



z. Verrucas none central, marginal i or 2 rows; cell about twice 



longer than wide . . . . . . '. . ovale, 57 



z. Verrucse none central, marginal i or two rows; cell less than twice 



longer than wide triplicatum, 73; Nordstedtii, * 



z. Verrucse centrally scattered, marginal in series of 3 each; semi- 

 cell quadrate, angles rounded . . triplicatiim, 73 

 aa. Central verrucse 3, in a single row; surface smooth, Donnellii, 71 

 aa. " 3, 2 above the base; punctate between, 



polymorphum.* 

 aa. " S, in 2 transverse rows, a row within the margin, 



quinarium.'* 

 ■aa\ " 6, in atriangle, apex toward the isthmus, 



polymazum, 70 

 aa. " 6 or 9, in 2 or 3 transverse rows; marginal rows 



I or 2; semi-cell semicircular, KiUhellii, 72; suborbicidare 78 

 aa. Central verrucas 10; semi-cell semicircular, end truncate, 



anisochondrwn, 7 2 

 aa. " circularly clustered; semi-cell twice longer than 



wide, sides emarginate, end truncate .... Seelyanum, 73 

 ib. Centre granularly rough and punctate; margin smooth; semi-cells 



oval . . . ..... tumidum, 61 



ib. Centre with 3 verrucas in a row; semi-cells semicircular, 



Do?inelln, 71 

 ib. Central verrucas i at the isthmus, 8 or 9 marginal in i or 2 curves, 



taxichondrum, 7 1 

 ib. " '■ '• 5 arched near the margin, 4 be- 



low these in the form of a cross .... bidcntulum.'^ 



bi). " 4 near the isthmus; semi-cells semicircular; end 



somewhat truncate; basal angles often pointed, 



pseudotaxichondrum, 7 1 

 ib. Central verrucas 7, i central, 6 below in a semicircle; ends retuse, 



smooth . . . . oculifermn.* 



ib. Central verrucse 19; 7 larger, central; 12 more or less distinct 



around them . . . . . . Amei-icanum.* 



cc. Chlorophyll diffused {dd). 



tc. " concentrated into i or 2 nuclei {ee). 



dd. Marginal verrucse or granules rounded (IiK). 

 dd. " " conical or pointed {ii). 



*r.-w. Alga;, p. 27 et seq. 



