78 University of Californi.a Publications in Botany [Vol.8 



no. -2206 of the Phycotheca Boreali-Americana agrees with the descrip- 

 tion, but is twisted above into a rope-like strand. It is also infested 

 with Lynghya cpiphytica Hieron. 



6. Lyng-bya semiplena (Ag.) J. Ag. 



Plant mass caespitose, mucous, about 3 cm. high, dull yellowish 

 green, sometimes becoming dark violet on drying ; filaments ascending 

 from a decumbent, entangled base, flexuous; sheaths hyaline, sub- 

 mucous, lamellate with age, 3/a thick; trichomes blue-green or yellow- 

 ish green, slightly attenuate at the apices, capitate, not constricted at 

 the joints, 5-12/x diam. (commonly T-lO/x,), cells 2-3/i, long, with 

 granules at the cross walls; apical cell provided with a depressed, 

 conical cah^ptra. 



Growing on rocks and on mud in the littoral belt. Puget Sound, 

 "Washington and San Diego County, California. 



J. Agardh, Alg. Mar. Medit. et Adriat., 1842, p. 11; Gomont, 

 Monogr. des. Oscill., 1892, p. 138 (1893, p. 158, Repr.) ; Collins, Holden 

 and Setchell, Phyc. Bor.-Amer. (Exsicc), no. 1905; Setchell and 

 Gardner, Alg. N.W. Amer., 1903, p. 187. Calothrix semipleoia Agardh, 

 Aufzahlung, etc., in Flora, vol. 10, 1827, p. 634. 



The type locality is Trieste at the upper end of the Adriatic Sea, 

 where it was found on rocks at the upper limits of the littoral belt. 

 As now recognized it is of wide distribution. It bears a close resem- 

 blance to Lynghya aestuarii especially to the narrower forms with 

 hyaline sheaths. Our specimens agree well with descriptions and 

 published specimens. 



19. Plectonema Thuret 



Trichomes provided with sheaths, with false lateral branching in 

 pairs or singly, caused by rapid growth in certain regions in the fila- 

 ments rupturing the sheaths, frequently constricted at the joints; 

 apices straight, rarely tapering, without calyptra ; sheaths hyaline, or 

 rarely colored. 



Thuret, Essai Class. Nost., 1875, pp. 375, 379. 



Thuret names Plectonema mirahile (Dillw.) Thuret first, and this 

 may be taken as the type of the genus. He also includes P. tenue 

 Thuret as the second member of the genus. Thuret {loc. cit.) places 

 Plectonenia between Symploca and Lynghya, on the one side, and 

 Scytonema and Tolypothrix, on the other. Gomont (1890, p. 5) places 



