110 THE AMERICAN MONTHLY [June, 



n. Surface without tooth-like elevations ; ei^ds rounded (o) . 



o. Cells in mucus, short, cylindrical or oval .... MesotcEiiium^ lo. 



0. Cells not or rarel}' in mucus Peniiijn^ 12. 



p. End viev^ 3-6 or more angular (r). 



p. End view not angular (i-) . 



r. Angles obtuse, acute, or with horn-like prolongations, Staurastrum^ 23. 

 s. Margins smooth, dentate or crenate ; no spines . . . Costnarhun^ 17. 



Species, 

 i. goxatozygon. 



1. Cells swollen at base, with 6 longitudinal lines of short setse, 



sex-spinifertim . * 



2. Cells not swollen at base {a). 



a. With hair-like spines clothing the surface pilosum^ 22. 



a. Without hair-like spines ; surface minutely roughened . asperum^ 22. 



2. Genicularia.* 



I. Cells 3^ to 6 times longer than broad ; granules in spirals. Americana.* 

 I. Cells 10-12 times longer than broad; granules scattered. spirotcenia.* 



3. Hyalotheca. 



1. Cells slightly constricted, length ^ the \vidth .... dissiliens^ 22. 



2. Cells slightly concave, length twice the width .... loidulata^ 23. 



3. Cells not constricted, margins straight ; sheath wide . . . mucosa., 23. 

 3. " " " •' sheath absent . . diibia., 24. 



4. Bambusina. 



1. Cells hub-shaped, somewhat longer than broad . . Brebissonii., 2^. 



2. Cells subcylindrical, 4 times longer than broad . . dclicatlssima., 25. 



5. Leptozosma. 

 An immature form of Desmidium. 6. 



6. Desmidium. 



I. Mucous sheath present cylbidricum., 25. 



I. Mucous sheath absent (a). 



a. Cells united bv their entire end margins {b^ . 



a. Cells united by the outer portions of the ends (</). 



b. Cells nearly twice as long as broad long-atiim^ 26. 



b. Cells less than twice as long as broad (c). 



c. Cells in side view quadrate . qitadratiim. 26 ; qnadrangulation^ 27. 



c. Cells in side view triangular Swartzii, 26. 



d. Borders crenate or undulate . . . aptogonhim., 27 ; diagomim^ 159. 

 d. Borders straight, filament twisted B alley i., 27. 



7. Phymatodocis. 

 But one species Nordstedtianuih^ 28. 



8. Sphjerozosma. 

 I. Cells twice broader than long, lobes not constricted {a). 



1. " " " " lobes constricted near the end, 



constrictum.* 



2. Cells twice longer than broad, in sheath or not . . . excavatum., 29. 

 2. Cells less than twice longer than broad ((5). 



a. Cells closely approximate, ends rounded pulchriim., 29. 



a. '^ " '^ ends truncate, concave . rectangiilare^ Ty\. 



a. Cells more or less remote, ends rounded .... vertebratjtm^ 30. 



b. Ends pointed ; semi-cells remote ; sinus deep, wide . tnoniliforme.\ 

 b. Ends rounded, spinous; cells slightly constricted . spinulosum.., 31. 



* Journ. R. Micr. Soc, Dec , 1885. + Bulletin lorrev Botanical Club, Dec, 1885. 



