Adiparva of Mahabharat tells us a story of Sage Dirghatamas fertilize the Queen of King Bali and gave birth five sons – Anga, Banga, Kalinga, Pundra & Sumha. by their names the janapadas were named. One can found other stories in various puranic texts related to this parts of
The name Bangla took shape much later in modern times. Pundra-Gour-Sumha-Rarh-Tamralipti-Samatat-Banga-Bangal-Harikel are some of the names of this parts of world.