THE CHLAMYDOBACTERIALES 303 



The following generic names must be considered: Chlamydo- 

 thrix, Clonothrix, Crenothrix, Detoniella, Didymohelix, Leptothrixy 

 Leptotrichia, Nodofolium, Phragmidiothrix, Sphaerotilus. 



The following key give the characters which are believed by 

 the writer to differentiate the genera which may be recognized. 



Key to the genera of Chlaniydohacteriaceae 



1. Filaments not usually permanently attached. 



a. Filaments straight, or at least not twisted Genus 1. Leptothrix 



b. Filaments twisted Genus 2. Didymohelix 



2. Filaments attached. 



a. Filaments unbranched Genus 3. Crenothrix 



b. Filaments show pseudodichotomous or false branching. 



(1) Swarm cells developed (motile conidia). Usually without a deposit 



of iron oxid in the sheath Genus 4. Sphaerotilus 



(2) Spherical, non-motile conidia. Usually with iron oxide. 



Genus 5. Clonothrix 



Genus 1. Leptothrix Kuetzing, 1843, p. 198 



Synonyms : 



Chlamydothrix Migula, 1900, p. 1030 

 Leptotrichia Trevisan, 1879, p. 138 

 Detoniella Trevisan, 1889, p. 929 



Filaments of cylindric colorless cells, with a sheath at first thin 

 and colorless, later thicker, yellow or brown, becoming encrusted with 

 iron oxide. The iron may be dissolved by dilute acid, whereupon 

 the inner cells show up luell. Multiplication is through the division 

 and abstriction of cells and motile cylindric swarm, cells. Swarm 

 cells sometimes germinate in the sheath giving appearance of branch- 

 ing. Pseudodichoto7nous branching may occur. 



The type species is Leptothrix ochracea (Leiblein) Kuetzing. 



There has been considerable confusion relative to the appro- 

 priate designation of this genus. The name Leptothrix was 

 created by Kuetzing for certain forms regarded as algae. The 

 first species named was L. ochracea, the Lyngbya ochracea of 

 Leiblein. Three other species were also described. Leptothrix 

 buccalis an organism from the mouth, was named by Robin in 

 1852. 



