144 



THE AMERICAN MONTHLY 



[August, 



and united in bunches or small fasci- 

 cles, like Syniploca (129). 



2. Filaments Jtaked^ or xvithout 

 distinct sheaths^ mostly with active^ 

 creeping movement. 



a. Filaments not curved like a 

 corkscrew. 



Synopsis of Genera. 

 Sheath very delicate or absent, cell 

 contents blue-green, movement ac- 

 tive. Oscillaria., 132. 

 Like Oscillaria^ but colorless. 



Beggiatoa. 133. 

 Like Oscillaria., filaments usuallv 

 very fine, motionless. 



Leptothrix^ 134. 

 Flexible, blue-green, moving. 



Spirzilina^ I35- 

 Like Spirjilina^ but colorless. 



Spirochcete^ 136. 

 132. Genus Oscillaria Bosc. 

 Filaments straight or cun'ed, 

 naked, or v\ath a very thin, scarcely 



discernable sheath ; cell contents (usu- 

 ally blue-green) colored. All mani- 

 fest a more or less active creeping 

 movement. 



133. Genus Beggiatoa Trevis. 

 Filaments as in Oscillaria., with 



active movement ; cell contents col- 

 orless, ^vith single, refracting granules 

 of reguline sulphur. 



134. Genus Leptothrix Kiitzing. 

 Filaments as in Oscillaria^ usually 



very fine, alw^ays motionless. 



b. Filaments cui"ved like a cork- 

 scre^\^ 



135. Genus Spirtdina Link. 

 Filaments flexible, with blue-green 



contents, and active Oscillaria-\ik.e 

 movement. 



136. Genus Spirochete Ehren- 

 berg. 



Filaments like those of Spirttlina., 

 with active movement, very fine, with 

 colorless contents. 



\_To be co7ittnued."\ 



S lateral, short, conical 

 Donnellii., 103. 

 . pingue, 105. 



Key to the Desmidieae. 



BY DR. A. C. STOKES. 



\_CotiiinHed from page /^/.] 



21. EuASTRUM. 



§ End lobe evidently distinct («). 

 § End lobe not evidently distinct (/;). 

 a. End lobe deeply notched (r). 



a. End lobe more or less concave (^). 



b. End deeply notched {e) . 

 b. End more or less convex semi-cell : with 7 or 



teeth 



b. End more or less convex ; sides without teeth 



c. Margins smooth («?). 

 c. Margins more or less spinous or beaded (_/") . 



c. Margins dentate (/^). 



d. Basal lobe deeply notched ; basal lobule broadly marginate ; central 



lobule obtuse m7{ltilobatum., 98. 



d. Basal lobe undulate (w). 



d. " rounded or angular (/). 



e. Margins smooth (>^). 



e. " cuspidate, spinulose or beaded (/) . 



f. Basal lobe undulate (w) . 



f. " I'ounded or angular (x). 



g. Margins smooth (/)". 



g. " cuspidate, spinulose or beaded (y). 



h. End lobes horizontal . . . Nordstedtianum., 105 ; spinosu?n, 106. 



h. " upright, diverging formosum., 103. 



