SPECIES OF DESMIDS. 91 



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



y. " more or less clustered on each semi-cell (ad], 



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



longer than wide ovale, 57 



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



longer than wide triplication, 73; Nordstedtii, * 



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

 cell quadrate, angles rounded triplication, 73 



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

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



polymorphism* 



aa. 5, in 2 transverse rows, a row within the margin, 



quinarium* 

 aa. 6, in a triangle, apex toward the isthmus, 



polymazum, 70 

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



i or 2; semi-cell semicircular, Kitchellii, 72; suborbiculare 78 

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



anisochondrum, 72 

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



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

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



oval tumidum, 61 



bb. Centre with 3 verrucae in a row; semi-cells semicircular, 



Donnellii, 71 



bb. Central verrucae i at the isthmus, 8 or 9 marginal in i or 2 curves, 



taxichondrum, 71 



bb. 5 arched near the margin, 4 be- 



low these in the form of a cross .... bidentulum* 

 b1>. " 4 near the isthmus; semi-cells semicircular; end 



somewhat truncate; basal angles often pointed, 



pseudotaxichondrum, 7 1 

 bb. Central verrucae 7, i central, 6 below in a semicircle; ends retuse, 



smooth oculiferum* 



bb. Central verrucae 19; 7 larger, central; 12 more or less distinct 



around them Americanum* 



cc. Chlorophyll diffused (dd). 



cc. concentrated into i or 2 nuclei (ee). 



dd. Marginal verrucae or granules rounded (M). 

 dd. " " conical or pointed (it). 



*F.-w. Algae, p. 27 et seq. 



