SYSTEMATIC AND DESCRIPTIVE. 1 87 



Genus III. Phragmidiothrix. 



Phragmidiothrix multiseptata. Cocci and 

 threads. The latter, 3 6 ^ in breadth, are sepa- 

 rated by transverse partitions into short cylindrical 

 discs, whose height is a fourth or sixth of their 

 breadth. Repeated transverse and longitudinal 

 division takes place in the discs, resulting in the 

 formation of cocci. The cocci have not been 

 observed isolated from the threads in a free state, 

 but they develop in situ into slender threads. In 

 addition to this continuous subdivision, Phragmi- 

 diothrioc differs from Beggiatoa in the absence of 

 sulphur, and from Crenothrix> by its wanting a 

 sheath. They occur attached to crabs (Gam- 

 marus locustd) in sea-water. 



Genus IV. Leptothrix. 



Leptothrix buccalis, Robin. Long, thin 

 threads, "71 /* broad, colourless, often united in 

 thick bundles or felted together. Masses of cocci 

 occur with the threads, and the threads themselves 

 are composed of long rods, short rods, and cocci. 

 The threads may break up into spiral-, vibrio-, and 

 spirochaete-forms. The last-named occur in large 

 numbers in the mouth, and have been named spiro- 

 chcete buccalis. The leptothrix buccalis is found 

 in teeth slime, and is believed to be intimately 

 connected with dental caries. The threads pene- 



