SPECIES OF DESMIDS. 83 



13. CLOSTERIUM. FIG. 13, a, b, C. 



Ends not or but slightly produced (i). 



Ends produced into long, often setiform, beaks (2). 



i. Cells straight or slightly curved; ends slightly tapering (a). 



i. " " * " " dorsum convex, ventrum nearly 



straight (g). 



i. Cells conspicuously curved; ventrum concave, with a central in- 

 flation (/). 



1. Cells conspicuously curved; ventrum without an inflation (/). 



2. Body margins equally convex; beaks longer than body, cetaceum, 47 

 2. " " " " beaks ^ as long as the body, 



pronum** 



2. Body margins not equally convex (m). 

 a. Length 5-12 times the width (b). 

 a. Length more than 12, less than 20 times the width (e). 



a. Length 20 times or more than the width (/). 



b. Ends suddenly contracted; cell fusiform, 5 times longer than wide, 



smooth nasutum, 41 



b. Ends not contracted, but tapering, acute; chlorophyll bands sev- 

 eral, granules in i row lanceolatum. 39 



b. Ends not contracted, rounded (c). 



b. " " " truncate (d). 



c. Cell slightly curved, small, 6-12 times longer than wide, smooth, 



acutum, 44 



c. " " " 5-10 longer than wide, smooth, obtusum, 38 



c. Cell nearly straight, decussately striate .... decussatum, 39 



c. " " " smooth, apices obtusely rounded, didymotocum* 



d. Cell slightly curved, 6-12 times longer than wide, striate; vacuole 



distinct didymotocum, 39 



e. Cytioderm with 4-5 longitudinal striae, often with 2 or 3 transverse 



bands and decussating striae angustatum, 40, 



e. Cytioderm striate; ends slightly incurved; globules about 20 in each, 

 semi-cell, axillary . , lineatum, 43 



e. Cytioderm striate; ends truncate, corners rounded; with three 



transverse sutures subdirectum.** 



f. Diameter 2jj, or less; smooth gracillima-lcevissima* 



f. Diameter 3-4/*; slightly curved, smooth, or with 1-4 trans, striae, 



subtile, 158 



f " 5~6/*; smooth gracile, 39 



/. " 10-16/1 (1). 



*F.-w. Algge. p. 23 et seq. **J. R. M. S., Feb. 89. 



