The atharvashiras preserved in the purANic texts

I just decided to record this note even though I did not complete the earlier one on the PBU. Upon reading my note on the PBU (as it currently stands), ekanetra made an inquiry regarding the atharvashiras upaniShad(ASU), which alludes to the ancient pAshupata vrata. ekanetra correctly noticed that at the heart of the ASU is the R^ik on which the bR^ihat sAman is composed. He wondered if this might have a connection with the sAman-s songs recited by the kApAlika-s as per the testimony of the sarva-siddhAnta viveka. Currently two versions of this famous pAshupata upaniShad are known, namely one preserved by the medieval commentator nArAyaNa and another by the commentator sha~NkarAnanda. But there is third version that has been much ignored. This is the version found in sections 2.17-18 of the li~Nga purANaM. This provides evidence, independent of these medieval commentators, that this upaniShad was indeed prevalent amongst the pAshupata-s. This paurANika version also preserves the R^igvedic mantra on which the bR^ihat is sung, suggesting that it was an integral part of the original mAheshvara system of the atharvashiras.