User Name Claim Type URI needed

I know there are many Claim Types (URI). For example, for email, the claim type URI is 

http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress

Is user name a Claim? If so, can anyone tell me what is the claim type URI for user name / logon name?

I am trying to add this a new claim type mapping, but couldn't find it anywhere. Please help.

Ven