98 SPECIES OF DESMIDS. 



r. Semi-cell subrectangular, basal lobe very broad, end lobe partly in- 

 cluded between the lateral . • . . crassum, 97 

 r. Semi-cell more or less pyramidal {s). 

 s. Diameter -j-i-j- in. or more (50-55/^) . . ... Everettense, 102 



J-. Diameter less then -j-i-^ in. ; apical angles acute, 



Porkornyanum, 104; erosum, 104 

 s. Diameter less than -g^ in.; apical angles rounded . elegans, 106 

 t. End lobe on a long slender neck; basal lobe with 6 protuberances, 



mammillosuni, 102 

 /. " " " " " " " basal lobe without protuberances, 



insigne, 102 

 t. End lobe not on a long neck [u). 

 u. Basal lobe much wider than end lobe (w). 

 u. " scarcely wider; diameter less than -g-J-j- in. {42 pi) 



simplex, 106 

 V. Basal sinus narrow, basal lobes approximate (f) 

 V. " wide, basal lobes widely separated . intermedium, 102 



f Diameter -j-^ in., (ioo/<) . . .... magnificum, ** 



f " less than -^\j^ in.; no pits on the surface, 



ansatum, gg\ purufn. ** 



|. " " " " " 4 pits on semi-cell . scrobiculatum, ** 



•w. End lobe beaded: angles of basal lobes beaded, ventricosum, 160 

 w. " dentate; angles of basal lobes dentate . simplex, 106 



w. " smooth, its angles spinous or cuspidate, rostratum, 106 



X. Angles of end lobe and margins of basal each with 3 diverging spines, 



cuspidatum, 105 



X. '' " with short spines, margins of basal dentate or 



granulate ..... . abruptum 107 



X. Angles of end lobe with one cusp or spine. . . rostratum 106 



y. Basal and central lobules both slightly emarginate, oblongum, 98 

 y. Basal lobes slightly emarginate, central obtuse, multilobatum, 98 



z. End lobe columnar, margins nearly parallel, end truncate, 



attenuatiim, 103 



z. End lobe not columnar, partly included between the lateral lobes, 



oblongum, 98 

 z. " " not included (aa). 



aa. Cell 2-3 times longer than broad; diameter -5^ in. (7SyM), 



humerosum, 99 



aa. Cell about twice longer than broad, diameter y^Vo ''^- (i4/<), 



Lundellii. 

 aa. " " " " diameter -j-^ in. (75/^), 



peciinatum.** 

 ** F.-W. Alg£E, p. 36 et. seq. 



