Additional information is from the "American Guide Series" of books, produced by the Federal Writers Project between 1935 and 1943.
Bus companies mentioned as only known to exist during 1930's, are mentioned in the American Guide Series, but not mentioned in the Mass Transportation's Directory.
Division Avenue Bus Line - connected Grand Rapids with Cutlerville, existed at least 1930's into 1950's.
Grand Rapids-Fremont Bus Line - existed in 1930's, possibly evolved to part of Decker Bus Line.
Grandville-Wyoming Transit Co. - connected Grand Rapids with Grandville, acquired in 1963 by Grand Rapids City Coach Lines.
Peacock Transit Lines - served Allendale, Eastmanville, Lamont.
True Blue - existed in 1930's.
Intercity Bus Line - connected Holland with Zeeland.
Lake Shore Line - suburban served Macatawa Park, Jension Park, Virginia Park, Central Park, Montello Park, Ottawa Beach, Waukazoo, Beachwood.
Jackson-Howell Bus Line - connected Jackson with Hudson MI and intermediate points.
Eberly Bus Service - connected connected Lansing with Bath, Park Lake, Tower Gardens. Possibly acquired during 1950's by Lansing Suburban Lines, which later renamed itself Lansing Metro Lines after also acquiring city transit operations in Lansing.
Holt-Lansing Lines - existed in 1930's.
Bolt Highway-Wolf Lake Transit Co. - connected Muskegon with Bolt Highway, Wolf Lake.
Muskegon Heights Motor Coach Co. - connected Muskegon with suburban district on Lake Harbor.
North Muskegon Bus Line - connected Muskegon with North Muskegon, Michigan State Park.
White Line Bus Co. - served Muskegon and suburbs.
Central Michigan Motor Coach Lines - existed in 1930's.
Midland Clare & Mt. Pleasant Bus Line - served Mt. Pleasant, Clare, Midland, Bentley.
Saginaw Valley Lines - suburban served Saginaw, Zilwaukee, Carrollton.
Stafford Motor - served Saginaw, existed in 1930's.
Thumb Bus - served Saginaw, existed in 1930's.
Mauzy Bus Line - existed in 1928, served Manistee to Filer City.
Petoskey-Harbor Springs Bus Line - existed in 1930's, possibly evolved to part of Harry Smith's Bus Line.
Copper Country Bus Line - served Calumet, Laurium, Ahmeek, Lake Linden, Hubbell, Mohawk.
Iron Mountain-Kingsford Transit Lines - city and suburban served Powers, Vulcan, Crystal Falls, Iron Mountain, Kingsford, Norway, Niagara WI.
Shubat Bus Co. - served Iron River, Stambaugh, Caspian, Gaston, Crystal Falls, Sagola, Iron Mountain.
Booth Transportation Line - served Sault Ste. Marie, existed in 1930's.
McGregor's Bus Lines - operated from St. Ignace to Manistique, sold to Northland Greyhound Lines in 1944.
Northern Line - served Marquette, existed in 1930's.
Canadian American Trailways - existed in 1930's.
Red Star Way Lines - existed in 1930's.
Bad Axe-Port Huron - existed in 1930's.
Bus companies operating over longer distances than the above suburban and interurban companies, but not listed in the Russell's Guide.
Great Eastern Bus Lines - existed in 1930's.
Hansen Motor Transit Co. - existed in 1930's.
Hiawatha Trails - existed in 1930's.