60 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



21. Cells joined by special apical processes Streptonema 



Cells joined by their flat apices or by flattened apical 



projections 22 



22. Cells short, in vertical view fusiform, triangular, or 



quadrangular (rarely circular with produced 



angles) Desmidium* 



Cells elongate, cylindrical Gymnosyga 



Description of Genera. 



Penium Breb. Cells straight, cylindrical or fusiform, 

 without median constriction, ends rounded ; free or collected 

 in a gelatinous membrane. Cell wall smooth, or minutely 

 granular, colorless or sometimes red, often finely striate. 

 Chloroplast axile ; when seen in cross section star-shaped, with 

 arms often forking. Multiplication by division, and by zygo- 

 spores formed by conjugation. 



P. closterioides Ralfs, Fig. 172. 



P. polymorphum Perty, Fig. 173. 



P. margaritaceum (Ehrb.) Breb., Fig. 175. 



P. Navicula Breb., Fig. 218. 



Roya West. Cells curved but not attenuated. Cell wall 

 without pores, chloroplast single, without dancing granules. 



R. obtusa (Breb.) West, Fig. 145. 



Closterium Nitzsch. Cells simple, elongated, crescent- 

 shaped or lunately curved, entire. The centres are not con- 

 stricted, but often bear a few transverse striae. The cell walls 

 are smooth or finely striate, colorless or brown ; at each end of 

 the cell is a vesicle, colorless or straw-colored, containing 

 numerous granules. The chloroplasts are arranged in longi- 

 tudinal rows broken in the middle by a transverse, colorless 



band. 



C. acuminatum Ktitz., Fig. 147. 



C. lanceolatum Kiitz., Fig. 148. 



C. Cucumis Ehrb. (?), Fig. 149. 



C. acerosum (Schrank) Ehrb. (?), Figs. 150, 151. 



C. Lunula Ehrb., Fig. 152. 



C. turgidum Ehrb., Fig. 153. 



C. strigosum Ehrb., Fig. 154. 



C. costatum Corda, Fig. 155. 



C. Delpontei Klebs, Fig. 156. 



