E. EUBACTERIALES FAMILY I--NITROBACTERIACEÆ--Proto- or autotrophic for N or C and sometimes for both (except Acetobacter). TRIBE I--NITROBACTEREÆ--autotrophic for C. Genus 1. _Hydrogenomonas_ Jensen, 1909. Type species, _Hydrogenomonas pantotropha_ (Kaserer, 1906) Jensen; oxidizes free H. Genus 2. _Methanomonas_ Jensen, 1909. Type species, _Methanomonas methanica_ (Söhngen) Jensen; oxidizes CH₄. Genus 3. _Carboxydomonas_ Jensen, 1909. Type species, _Carboxydomonas oligocarbophila_ (Beijerinck and Van Delden, 1903) Jensen; oxidizes CO. Genus 4. _Acetobacter_ Fuhrman, 1905. Type species, _Acetobacter aceti_ (Thompson, 1852) Fuhrman; oxidizes alcohol to acetic acid. Genus 5. _Nitrosomonas_ Winogradsky, 1892. Type species, _Nitrosomonas europoea_ Winogradsky; oxidizes ammonia or ammonium salts to nitrous acid, hence nitrites. Genus 6. _Nitrobacter_ Winogradsky, 1892. Type species, _Nitrobacter Winogradskyi_ Committee of 1917; oxidizes nitrous acid (nitrites) to nitric acid (nitrates). TRIBE II--AZOTOBACTEREÆ--prototrophic for N. Genus 7. _Azotobacter_ Beijerinck, 1901; large, free-living, aerobic N absorbers. Type species, _Azotobacter chroococcum_ Beijerinck. Genus 8. _Rhizobium_ Frank, 1889. Type species, _Rhizobium leguminosarum_ Frank; root tubercle bacteria of legumes. FAMILY II--PSEUDOMONADACEÆ, Committee of 1917. Genus 1. _Pseudomonas_ Migula, 1894. Type species, _Pseudomonas violacea_ (Schroeter, 1872) Migula. FAMILY III--SPIRILLACEÆ Migula, 1894--all spiral bacteria. Genus 1. _Vibrio_ Müller, 1786, emended by E. F. Smith, 1905. Type species, _Vibrio choleræ_ (Koch, 1884) Schroeter, 1886. Genus 2. _Spirillum_ Ehrenberg, 1830, emended Migula, 1894. Type species, _Spirillum undula_ (Müller, 1786) Ehrenberg. FAMILY IV--COCCACEÆ Zopf, 1884, emended Migula, 1894--all cocci. Tribe I--NEISSEREÆ. Genus 1. _Neisseria_ Trevisan, 1885. Type species, _Neisseria gonorrhoeae_ Trevisan. Tribe II--STREPTOCOCCEÆ Trevisan, 1889. Genus 2. _Diplococcus_ Weichselbaum, 1886. Type species, _Diplococcus pneumoniae_ Weichselbaum. Genus 3. _Leuconostoc_ Van Tieghem, 1878. Type species, _Leuconostoc mesenterioides_ (Cienkowski) Van Tieghem. Genus 4. _Streptococcus_ Rosenbach, 1884; emended Winslow and Rogers, 1905. Type species, _Streptococcus pyogenes_ Rosenbach. Tribe III--MICROCOCCEÆ Trevisan, 1889. Genus 5. _Staphylococcus_ Rosenbach, 1884; animal parasites.