They are said to be originated from The Mahabharata Tribe - Mahishaka (महिषक) Mentioned in Geography of Mahabharata (VI.10.57). Branches of Nagavansha are - 1. Bish/Bains 2. Taxak 3. Aulak 4. Kalkal 5. Kala/ Kalidhaman/ Kalkhande 6. Meetha 7. Bharshiv 8. Bharaich.
Bhim Singh Dahiya writes with reference to Heornle and Cunningham that Harshavardhana belonged to this clan. He is connected with Shrimalpur which is a village on the border of Hoshiarpur and Jullundhar districts in Punjab and is nowadays called Māhalpur. Even today it is inhabited by Bish clan of Jats.  They are mentioned in Mahabharata along with Khatkal, Karaskar, Mahishaka, Karkana and Viraka, by their Sanskrit name Mahisha which becomes or Bish or Bains in Indian languages of english word bufallow.  Bish is one of 36 royal clans in India along with Salar, Dahima etc. 
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