FAMILY PHAGACEAE 1129 



d'Herelle (loc. c?^, 345), presumably the type species of this genus, was not an ordinary 

 virus but was said to be non-parasitic (i.e., free-living) in nature, was capable of re- 

 ducing sulphur, and is not now identifiable. The genus name Protobios and the cor- 

 responding binomial Protobios bacteriophagus d'Herelle are therefore regarded also 

 as nomina diibia and are not used here. Bacteriophagus Thornberry (Phytopath., SI, 

 1941, 23) appears to represent a variant spelling of d'Herelle's earlier genus name; it 

 was not accompanied by any indication of what recognizable single bacteriophage 

 served as type and thus does not modif}' the standing of Bacteriophagum. 



Key to the species of genus Phagus. 

 I. Dj'sentery-coli bacteriophages. 



A. Producing large plaques, 8 to 12 mm in diameter. 



1. Particle size small, 8 to 12 millimicrons. 



1. Phagus minivnis. 



2. Particle size 15 to 20 millimicrons. 



2. Phagus minor. 



B. Producing moderately large plaques, 2 to 6 mm in diameter, with distinct 



halo. 



1. Particle size 20 to 30 millimicrons. 



3. Phagus parvus. 



4. Phagus primarius . 



5. Phagus secundarius. 

 G. Phagus dysenteriae. 



C. Plaques medium size, 1 to 3 mm in diameter, with distinct halo. 

 1. Particle size 25 to 40 millimicrons. 



7. Phagus medius. 



8. Phagus astrictus. 



D. Plaques small, 0.5 to 1.5 mm in diameter, with soft edge or narrow halo. 

 1. Particle size 30 to 45 millimicrons. 



9. Phagus major. 

 10.' Phagus coli. 



11. Phagus artus. 



E. Plaques very small, 0.1 to 1.2 mm in diameter, with sharp edges. 

 1. Particle size 50 to 75 millimicrons. 



12. Phagus maximus. 



II. Bacteriophages attacking Agrobacterium tumefaciens Conn, Pseudomonas 

 solanacearum Smith, Xanthomonas citri Dowson, Xanthomonas pruni 

 Dowson, Erwinia carotovora Holland, Erwinia aroideae Holland, Bac- 

 terium stewarti E. F. Smith. 



