31. Spherical cells 1 to 2 microns in diameter, 2 to 60 or more cells occurring in a primary capsule 10 to 20 microns wide; secondary capsules unite to form a mucilaginous colony; iron or manganese compounds are stored in the secondary capsules. Siderocapsa p. 218 Cells coccoid to ovoid, 4.8 to 5.0 by 6.5 microns, forming short chains embedded in a thin mucilaginous layer; iron compounds stored in the surface membrane of the cells Sideronema p. 220 Cells rod-shaped, 2.5 by 6 to 15 microns, straight or slightly bent; not encapsulated; iron or manganese stored on the surface or in the membrane of the cell Siderobacter p. 226 32. Strict intracellular parasites occurring in the cytoplasm of conjunctival cells in cattle, goats and sheep. Elliptical, coccoid, rod-shaped and comma-shaped cells occur Colettsia p. 961 (See Manual keys for the class Microtatobiotes) p. 933 Spherical cells produced in macroscopic fruiting bodies on decaying vegetable material or in culture; fruiting bodies sessile or nearly so. The cocci germinate to produce rod-shaped cells which glide on a solid surface; not flagellated Myxococcus p. 883 Or Chondrococcus p. 886 (See Manual keys for the order Myxobacterales) p. 858 Pleomorphic cultures consisting of large and small cocci and small rod-shaped cells which are motile by means of a single polar flagellum; strongly halophilic, requiring 20 to 30 per cent salt for optimum growth; Gram-negative Halobacterium (H. cutirubrum) p. 207 Not as above 33 33. Cells spherical to ovoid, varying from spheres 5 microns in diameter to large cylindrical organisms 35 to 100 microns long; sulfur deposited internally when growing in the present of hydrogen sulfide. In one of the two recorded species, large crystals of cal- cium carbonate fill the cells; motile with a slow jerky rotating action when in con- tact with solid surfaces Achromatium p. 852 Cells spherical to ovoid, 5 to 20 microns in diameter, with the cytoplasm compressed in one end of the cell; sulfur deposited in the cytoplasmic layer; exhibits an extremely rapid darting motion in free solution suggestive of flagella, which have never been demonstrated; found in waters containing hydrogen sulfide, forming a tenacious web-like growth in a zone of critical hydrogen sulfide-oxygen concentration Thiovulum p. 81 Not as above 34 34. Cocci varying in diameter from 0.5 to 4.0 microns; grow in a mineral salts bicarbonate medium with formate as the only known source of available carbon, fermenting it to methane, CO2 and possibly hydrogen; pH range, 7.4 to 9.2 Methanococcus p. 1^73 (M. vannielii) Not as above 35 35. Spherical cells 36 Rods, curved or straight 43 36. Arranged in cubical packets Sarcina p. Ifil Not as above 37 37. Motile by means of peritrichous fiagella 38 Non -motile 40 38. Gram-positive; cells occur in irregular clusters Micrococcus p. 1^55 (M. cryophilus) Gram-negative 39
