470 R. E. BUCHANAN 



loosely, the gelatin is swollen, and the cells swarm out singly and 

 rather irregularly. 



The type species is Thiothece gelatinosa Winogradsky. 



Genus IV. Thiopolycoccus Winogradsky, 1888, p. 79 



Families solid, non-motile, consisting of small cells closely 

 appressed. Multiplication of the colonies by the breaking up of 

 the surface into numerous short shreds and lobes which continue to 

 split up into smaller heaps. Cells red. 



The type species is Thiopolycoccus ruber Winogradsky. 



Tribe V. Chromatieae Trib. nov. 



Synonym : 



Chromatiaceae Migula, 1900, p. 1047 



Sulphur bacteria in which the cells are not united into families, 

 but free, and capable of swarming at any time. 



The genera of the tribe Chromatieae may be differentiated by 

 the following key: 



Key to the genera of Chromatieae 



A. Cells motile by means of polar flagella. Elongated. 

 I. Cells not spiral. 



a. Cells cylindric Genus I. Chromatium 



b. Cells with tendency to spindle shape Genus II. Rhabdomonas 



II. Cells spiral Genus III. Thiospirillum 



•B. Cells spherical, or little elongate, non motile. 



I. Cells not encapsulated Genus IV. Rhodocapsa 



II. Cells encapsulated in pairs Genus V. Rhodothece 



Genus I. Chromatium Perty, 1852 



Synonym : 



Rhodomonas Jensen, 1909, p. 334 



Cells cylindric-elliptical or relatively thick cylindrical. Cell con- 

 tents red, containing dark sulphur granules. Cells somewhat vari- 

 able in shape, straight, more or less bent, short cells ovoid and 

 longer forms more cylindrical. Motile by means of polar flagella. 



The type species is Chromatium okenii Perty. 



