1886.] MICEOSCOPICAL JOUKNAL. 109 



Key to the Desmidieae. 



BY DR. A. C. STOKES. 



The following artificial key refers almost exclusively to the forms described 

 in the Rev. Francis Wolle's ■• Desmids of the United States.' In the table 

 of genera the figures appended to each name direct to that genus in this list ; 

 those after the specific names to the pages of Mr. Wolle's work, where the 

 descriptions and references to the illustrations will be found. 



Genera. 

 § Cells united into filaments (a). 

 § Cells not united into filaments (^) . 

 a. In a transparent, jelly-like sheath (6). 



a. Not in a jelly-like sheath (d). 



b. Cells with 2 teeth on each narrow end Dcsmidinni^ 6. 



b. Cells deeply constricted, almost into two parts (c). 



b. Cells not deeply constricted, and without teeth . . . Hyalotheca^ 3. 



c. With ' claspers ' across the sutures OuycJionema^ (^. 



c. Without *• claspers ;' cells united by a narrow isthmus SpJuvrozosina^ 8. 



d. Band not twisted ; cells w^ith "■ claspers ' across the sutures, 



Ofiyc/wJienia, 9. 

 d. " *•' cells without *■ claspers ' {e) . 



d. Band twisted ; cells triangular or quadrangular . . . Desmidiiini^ 6. 



e. Cells barrel or hub-shaped, with i or 2 median bands Banibtisina^ 4. 

 e. " " " without bands, the sutures projecting, 



Leptozosnia^ =5. 

 e. Cells cylindrical, sometimes swollen at base (/") • 

 e. Cells quadrangular, deeply constricted, often .slightly twisted, 



Phymatodocis^ 7. 

 f. Ten to 30 times longer than broad Gonatozyg-on^ i. 



f. Three to 6 times longer than broad Genicidaria, 2. 



g. Cell more or less crescentic Closteriiun, 13. 



g. Cell cylindrical, fusiform, dumb-bell or hour-glass shaped (/). 



g. Cell flattened; orbicular, oblong, or elliptical {h) . 



h. Mostly orbicular or broadly elliptical ; centre deeply constricted, the semi- 

 cells 3-5 lobed, the lobes entire or variously incised, Micraster'ias^ 22. 

 h. Mostly oblong or elliptical ; margins wavy, the depressions rounded ; ends 



. usually notched or incised Euastrutn^ 21. 



/. Cell constricted in the middle ; no arms nor spines (y) . 

 i. '' " '' with arms or spines (/) . 



i. Cell not constricted ; no arms nor spines (w). 



j. Cell cylindrical, ends simply notched Tctniemorus^ iS. 



j. *■' '' ends rounded, truncate or divided (/'). 



j. Cell more or less dumb-bell — or hour-glass shaped (/) . 



k. Cell 6 to 30 times longer than broad Docidium^ 14. 



k. Cell 2-5 times longer than broad ; ends rounded . Calocylindrus^ 16. 



I. Arms 2, 3 or more, radiating Staurastrimi. 23 



/. Arms none ; semi-cells with a central, rounded, truncate or denticulate 

 tubercle ; spines usually numerous and marginal, XaiitJiidium^ 19. 

 /. Arms none ; no central tubercle ; spines 4 or 8, \yNO on each end, \ 

 I. "■ '' '' spines 16, four on each end, j 



Arthrodesniiis ^ 20. 

 tn. Chlorophyll in one or more spiral bands .... Spirot<^nia^ 11. 

 m. " not in spiral bands («). 



n. Surface rough with tooth-like or rounded elevations . Triploceras. 1^. 



