In the early 1900’s, the larger of the two Manhattan streetcar systems was the Metropolitan Street Railway system, which was a bit of a house of cards that broke up in part after bankruptcy in 1908. The core company became the New York Railways system, which passed to the New York Railways Corporation, which operated under this name from 1925 to 1936.
The New York Railways Corporation was controlled by the Fifth Avenue Coach Company (and therefore ultimately by General Motors, which operated the Fifth Avenue Coach Company. In 1925, the New York Railways acquired control of the Manhattan Surface Coach Company, which was re-named the New York City Omnibus Corporation from 1930 to 1956.
The streetcar lines were converted to bus in 1936, when the New York Railways Company was liquidated and control passed to Fifth Avenue Coach and The Omnibus Corp. So as of 1936 the Fifth Avenue Corporation and NYC Omnibus systems were under common control.