302 FRESH-WATER ALG^ OF THE UNITED STATES. 



LYNGBYA CATARACTA, (Eab. ) Wolle. 



Forms a thick, firm gelatinous, extended stratum, meas- 

 uring one-half inch, more or less, in thickness ; pachyder- 

 mate ineinbranaceous, bluish-green, velvety ; trichomes 

 slightly curved, articulations shorter than the diameter. 

 Apices straight, obtuse or rarely barbed. 



Diameter of filaments, 3-3. 5 yw. 

 Syn. Phormidium cafaractum, Eab. 



Frequent at waterfalls, mill dams, etc., sometimes in 

 cushion-like masses, two or more inches in thickness; ordi- 

 narily not so thick, but 6-12 inches in extent. 



Plate CCII, figs. 18, 19, from a Pennsylvania specimen. 



LYNGBYA EETZII, (Ag.) Kg. 



Stratum broadly expanded, rather compact, green-blacjt 

 or deep olive, shining, parts changing to brownish, shortly 

 radiating ; trichomes rather straight, bright aeruginous, 

 indistinctly articulate ; articles about half as long as wide ; 

 apices slightly attenuated, obtuse, straight. 



Diameter of filaments, 4-5.5 yw. 



Syn. Oscillaria Retzii, Ag. ; 0. laevigata, Yauch. ; Phormidium 

 Retzii, Kg. 



Wet soil, South Carolina; wet rocks, Charlotte, Vermont. 

 Plate CCII, figs. 15-17, from marsh grounds. 



LYNGBYA PAPYRINA, (Kg. ) Kirch. 



Stratum thin paper like, sometimes shortly radiating, with 

 a pallid or brownish fibrillose substratum, formed from the 

 interlaced empty sheaths; trichomes equal, joints nearly 

 equal or a little shorter than their diameter ; granulated at 

 their junction, apex obtuse, straight. 



Diameter of trichomes, 5-7 yw ; with sheath, 7-9 yw. 



Syn. Oscillaria papyrina, Bory ; Phormidium papyrinum. Kg. ; 

 Ph. papyraceum, Eab. ; very near also to L/yngbya vulgaris. 

 Plate CCII, figs. 9-11, specimen from the vicinity of New 

 Haven, Connecticut. 



LYNGBYA INTERRUPTA, (Kg. ) 



Forming a membranaceous, aeruginous-green, mucous 

 stratum, scarcely radiating ; substratum somewhat membra- 

 naceous, decolored ; trichomes flexuously curved, yellowish 

 green, interrupted; sheath continous firm; articulations 

 half as long as wide, homogeneous or finely granulate at 

 joints; apices straight, obtuse. 



Diameter, 5-7 yw. 



