SPECIES OF DESMIDS. 83 



13. CLOSTERIUM. FIG. 13, a, 6, 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, f^/a^^«OT, 47 

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



2. Body margins not equally convex (m). 



a. Length 5-12 times the width (6). 



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



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



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

 smooth . ..... nasuium, 41 



d. 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, 



acututn, 44 

 c. " " " S-io 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 strise, often with 2 or 3 transverse 



bands and decussating stri« . . . angustatum, 40 



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



semi-cell, axillary , ... Itneahan, 43 



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



transverse sutures ... subdirectum.** 



f. Diameter 2/< or less; smooth gracillmia-lmvissinui* 

 f. Diameter 3-4yU; slightly curved, smooth, or with 1-4 trans, strias, 



subtile, 158 



/ " 5-6/^; smooth . gracile, 39 



/ " io-i6/i (1). 



*F.-w. Algee. p. i^etseq. **J. R. M. S., Feb. 8g. 



