84 SPECIES OF DESMIDS. 



/. Diameter 18//; about 30 times as long as wide, smooth, ends 



rounded . . . . . ... . . Brebissonii* 



f. " 20-21/^; striated, ends rounded . ... prelongum* 



f. " 36/i; about 20 times as long as wide, smooth, ends not 

 curved . . . . . ensis* 



T Surface smooth; slightly tapering from the middle . strigosum, 42 

 Tf " longitudinally striate only; diam. 11-12//, juncidum, 38 



^ " " " with 1-4 trans, striae; diam. 12-13//, 



7nacilentum, 38 



g. Ends inclined upward at a dorsal depression; ventrum slightly con- 



cave; strise fine, numerous . turgidum, 41 



g. Ends suddenly contracted to a narrow point; cell slightly curved, 



attenuatum, 41 

 g. Ends not suddenly contracted (/%). 

 h. Cytioderm deeply striate; distinctly granulate or areolate, 



areolatum, 43 

 h. " more or less distinctly striate; cell linear-fusiform, 



15-24 times longer than wide . . acerosum, 41 



h. Cytioderm 9-12 longitudinally costate; cell fusiform, 4-5 times 



longer than wide . . . subcostatum* 



h. Cytioderm more or less distinctly striate; cell semi-lunar, 5-6 times 



longer than wide . ... Lunula, 40 



i. Diameter -j-i-ij to -j^ in. (75-110//); cytioderm smooth, 



Ehrenbergii, 45 

 /. Diameter j-^to -j-|-g- in. (40-60//); globules a single row, 



moniliferum, 45; Leibleinii, 46 

 i. " " " cell curved, rapidly tapering into 



narrow, somewhat upwardly-curved ends; cell 6-8 times 



longer than wide . Ralfsii, 46 



i. Diameter ^l-g^ to 3-|^ in. (35-45//); 2 or 3 sutures in the middle; 



about 20 times longer than wide. . . . Delpontii* 



j. Cytioderm with many distinct striae; length 6-16 times the width; 



vacuole large .... . . striolaium, 42 



j. Cytioderm with fine striae; length 12-16 times the width; vacuole 



small . . decorum, 43 



J. Cytioderm with 5-8 distinct striae; length 6-8 times the width; 



vacuole large . . . costatum, 42 



j. Cytioderm smooth; cell crescent-shaped, often subsemicircular {Ji). 



j. " " cell not conspicuously crescent-shaped (/). 



k. Ends separated 7-10 times the diameter; width y^Vo" ^o tAt ■'i- 



(i6-20/<) ... ... . . ... Diance, 44 



*F.-w. Alg^, p. 23. 



