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



Arthrospira Stiz. Filaments cylindrical, commonly de- 

 void of a sheath, and twisted into a regular spiral. The latter 

 character is the only distinction from Oscillatoria. 



A. Gomontiwia Setchell. We have not found this species, 

 but Setchell has mentioned it as occurring in Bridgeport. 



SUB-FAMILY II. VAGINARIE^E 



Blue-green Algae, which lack heterocysts, and are distin- 

 guished by having one or more trichomes in the same sheath. 

 This sheath is often branched, may be lamellose and colored, 

 or mucous and uncolored. 



Description of Genera. 



Microcoleus Desm. (Cthonoblastus Kiitz.). Trichomes 

 like Lyngbya, except that two or more are often enclosed in 

 one sheath, which is at first closed at the end, and later breaks 

 open, sometimes dividing into shreds. The sheath is colorless, 

 not lamellose, large, seldom indistinct. 



Schizothrix Kiitz. (Inactis Kiitz. ; Hyphaeothrix Kiitz., 

 in part). Sheaths firm, lamellose, hyaline or colored, and 

 containing few or many trichomes. 



[S. lardacea (Cesati) Gomont ; 5\ coriacea (Kiitz.) 

 Gomont.] 



FAMILY II. NOSTOCACE^. 



Cells spherical or oval, arranged in simple chains, or, 

 rarely, with spurious branches. The chain is imbedded in a 

 more or less copious jelly. Some genera are provided with 

 spores and heterocysts. The heterocysts are yellow, straw- 

 colored, or nearly colorless, and are situated at the end of the 

 chain, or between two vegetative cells. Their function is un- 

 known. The dark green, granular spores divide after a period 

 of rest, and then germinate. Many are terrestrial. 



Key to Genera. 



i. Filaments contorted, within a definite gelatinous 



tegument A r ostoc* 



Filaments more or less straight, free or in a formless 

 slimy mass, not inclosed in a tegument 2 



