1919 J SetchcU-Gardncr : Myxophyceae 93 



Bornet, in Bornet and Thuret, Notes Algol., 1880, p. 86, pi. 28, 

 figs. 1-12 ; Bornet and Flahault, Rev. IV, 1888, p. 192 ; Setchell and 

 Gardner, Alg. N.W. Amer., 1903, p. 189 (growing in fresh water). 

 Rivularia Linckia Roth, Neue Beitriige znr Botanik I, 1802, p. 265. 



Onr specimens form shapeless expansions, with mnch contorted 

 trichomes and with excellent spores. They certainly seem to be Nostoc 

 Linckia and their occurrence in salt water is worthy of note. 



. FAMILY 5. BIVULARIACEAE rabenhorst 



Filaments cohering by their gelatinous sheaths, forming more or 

 less definite spherical or hemispherical colonies and radiating from 

 the center outward, or parallel and forming more or less penicillatc 

 or caespitose strata, or rarely solitary, simple or branched, composed 

 of sheaths and a single series of cells; trichomes usually much attenu- 

 ated and terminated by a hair, one to several within a slieath ; hetero- 

 cysts basal and intercalary, rarely absent; branching false, usually 

 beneath the heterocysts, more rarely between the heterocj'sts ; multi- 

 plication by hormogonia. hzr resting spores or by both. 



Rabenhorst, Fl. Eur. Alg., vol. 2, 1865, pp. 2, 200 (pro max. parte). 

 Rivularieae Harvey, in W. J. Hooker, Brit. Fl., vol. 2, part 1, 1833, 

 p. 391 (pro parte). 



The Rivulariaceae form a very natural family distinguished by 

 a combination of false branching and terminal hairs. Usually 

 heterocysts are present, but occasionally they are lacking. In the 

 Rivulariaceae as previously distinguished, the opposite ends of the 

 trichomes are unlik(% but in Hammataideu {Ammatoidea, "W. and G. S. 

 West, 1916, p. 46) both ends of the trichome terminate in a hair wliile 

 the central portion of the trichome is bent at nearly right angles to 

 the end portions and is devoid of heterocj'sts. It seems to us that 

 H<imnvatoidea bears the same relation to the non-heterocysted species 

 of Calothrix that the subgenus Leibleinia does to the typical species 

 of Lynghyo. Also there is a heterocysted species of Calothrix (C 

 pilosa Harv.) whose central portion is decumbent and both ends erect. 

 We have removed the genus Brachytrichia from Rivulariaceae to 

 Stigonemataceae on account of its true branching, although it possesses 

 hairs. 



The members of the Rivulariaceae are more largely marine than 

 those of any other family of the Myxophyceae, yet there are many 

 fresh water species in the family. The representation of the Rivu- 



