96 SPECIES OF DESMIDS. 



20. Arthrodesmus. Fig. 20, a, b. 



I Cytioderm smooth {a). 



§ Cytioderm verrucose or spinous (V). 



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 . guadridens, 96 

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



c. Spines on the same side diverging (e). 

 £. " " parallel {g). 



c. " " converging . . convergens, 95 



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



octocornis, 97 



e. End truncate; spines widely divergent . . . Incus, 97 



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



f. Diameter of cell -j^ (40/') • incrassatus* 



f. " " 8^ — tk (3°-3S/^) • • • subulatus, 96 

 /. " " -rh^ (2°/<) o^'alis, 96 



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

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

 g. " semi-cell orbicular, diameter -^-gij-jj- (i2/(), 



orbicularis 96 

 g, " semi-cell elliptical; spines often very short, 



convergens var., 95 

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



triangtdaris, 36 



^^ 



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 (^.) 



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 (</.) 



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

 c. Margins dentate (K). 



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

 **F. W. Aigse, p. ■i^etseq. 



