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







clustered in gelatinous masses, or single. Cells spherical or 

 nearly so, some of them changing into brownish elongated 

 spores, which are solitary, or one on either side of a heterocyst, 

 or, rarely, in a short series. Heterocysts not terminal. 



A. gigantea Wood, Fig. n. 



A. Flos-aqua? Kiitz, or circinalis (Rab.) Kirch., Fig. 12. 



[A. osciUarioides Bory.] 



A nab ana is very common in reservoirs, and sometimes in 

 combination with Microcystis is so abundant as to give the 

 water a very bad taste and smell, and a distinct color. It is 

 one of the most troublesome Algae in our city reservoirs. 



FAMILY III. SCYTONEMACEJE. 



This family is known by its method of branching. Each 

 filament is enclosed in a sheath of uniform thickness, and at 

 intervals penetrates this sheath to form long, flexuose branches 

 which are provided with their own sheaths. The filaments are 

 cylindrical, but thickened toward the growing end, and con- 

 tain heterocysts. The sheath may be colorless, or yellow, or 

 brown. Reproduction is usually by hormogones. though in 

 some species spores are produced. 



Key to Genera. 



Branches in pairs, rising between the heterocysts 



Scytonema* 

 Branches single, rising in the region of the heterocysts 



Tolypothrix* 



Description of Genera. 



Scytonema Ag. (Petalonema Berkeley; Schizosiphon 

 Kiitz., in part; Symphyosiphon Kiitz., in part ; Athrosiphon 

 Kiitz.). Each filament enclosed in a sheath ; branches in pairs 

 produced by a fold of the filament, which breaks through the 

 sheath between the heterocysts. The heterocysts are scattered 

 irregularly throughout the filament. The filaments produce in- 

 terwoven mats of larger or smaller size. The sheath is lamel- 

 lose, and yellow or brown in color, generally of an even thick- 

 ness, but occasionally the margins are irregular. 



[S. crispum (Ag.) Bornet ; 5\ Hofmanni Ag. : S. myoch- 



