304 R. E. BUCHANAN 



These facts have led to the development of three conceptions 

 of the genus as follows: 



1. L'eptothrix. A genus of bacteria with the L. ochracea as the 

 type. 



2. Leptothrix. A genus of bacteria with L. buccalis as the type. 



3. Leptothrix. A genus of algae. In this sense the genus has 

 been recognized by many algologists. However, it may be 

 noted that by recent writers (as in West's British Fresh Water 

 Algae) the genus Leptothrix is made a synonym of Lyngbya. 

 Many authors include L. ochracea with the algae. 



Inasmuch as Leptothrix ochracea was definitely first named in 

 this genus, it would seem to be entirely appropriate to make it 

 they type of the genus. 



It should be noted that this renders Leptothrix as applied to 

 organisms such as L. buccalis quite invalid. 



Genus 2. Didymohelix Griffith, 1853, p. 438 



Synonyms: 



Gaillonella Bory, 1823, in part 

 Gallionella Ehrenberg, 1838, p. 166, in part 

 Gloeotila Kuetzing, 1843, p. 245, in part 

 Spirophyllum ? Ellis, 1907, p. 516 

 Nodofolium ? ElHs, 1910, p. 321 



Filament tivisted, simple, or two filaments, twisted together. 

 Young cells colorless, later yellow brown to rust red through deposi- 

 tion of iron. Simple filaments show no division into cells, even 

 when iron is removed with acid and stain applied. Sheath not 

 demonstrable. 



The type species is Didymohelix ferruginea (Ehr.) Griffiths. 



The generic name Gallionella was first used by Ehrenberg as a 

 revised spelling of Gaillonella, a genus of diatoms created by 

 Bory de St. Vincent. Ehrenberg included several true diatoms 

 in the genus, together with this form, which he erroniously 

 believed contained silicon, and to be a diatom. Gallionella is a 

 valid diatom genus (or subgenus of Meloseira according to some 

 authors), and should not be used as a generic name for bacteria. 



