96 SPECIES OF DESMIDS. 



20. ARTHRODESMUS. FIG. 20, a, b. 



Cytioderm smooth (a). 



Cytioderm verrucose or spinous (b). 



a. Semi-cell with 2 spines (c). 



a. Semi-cell with more than 2 spines (d). 



b. Cytioderm with deciduous spines Rauii, 95 



b. " verrucose in rows, margins crenate . quadridens, 96 



b. " " " ends alone crenate, notochondrus** 



c. Spines on the same side diverging (<?). 

 c. " " parallel (g). 



c. " " converging convergens, 95 



d. Margin of semi-cell angular, each angle with i or two spines, 



octocorniS) 9 7 



e. End truncate; spines widely divergent Incus, 97 



e. End convex; spines moderately divergent (/). 



f. Diameter of cell 7r | T (40 yw) incrassatus* 



/ " " s^ rhr (3-35 /') subulatus, 96 



/. " -nW (20^) watts, 96 



g. Nuclei, 2 in each oblong-oval semi-cell fragilis, 95 



g. Nuclei none; semi-cell oval, diameter T ^-y in. (20yu) . ovalis, 96 

 ^. " semi-cell orbicular, diameter ^^Q- (i2yu), 



orbicularis 96 

 ^. " semi-cell elliptical; spines often very short, 



converge 'ns var., 95 

 g. " semi-cell triangular, sinus wide, isthmus cylindrical, 



triangular is, 3 6 * * 



21. EUASTRUM. FIG. 21. 



End lobe evidently distinct (a). 

 End lobe evidently not distinct (b). 

 a. End lobe deeply notched (c). 



a. End lobe more or less concave or sometimes convex (g.) 



b. End deeply notched (e). 



b. End more or less convex; semi-cell with 7 or 8 lateral, short, coni- 

 cal teeth Donnellii) 103 



b. End more or less convex; sides without teeth . . pingue, 105 



c. Margins smooth (d.) 



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

 c. Margins dentate (7z). 



*Journ. R. Micr. Soc., Feb., 1886. 

 **F. W. Algae, p. 34 et seq. 



