शिशुमार-चक्र
The Śiśumāra-cakra is the arrangement of planets and constellations which the Puranas see in the sky in the shape of a śiśumāra, a dolphin or gharial, with Dhruva fixed at the tip of its tail; the fifth Skandha of the Bhagavata describes it at length and calls it a luminous form of the Lord. At SB 2.2.24 it is a stage on the upward road of the yogi: travelling the brahma-path of the suṣumṇā and passing Vaiśvānara, his impurity washed away, he reaches this circle set 'above Hari', and thence, crossing even the navel of the universe, proceeds to Maharloka (SB 2.2.25).
Śrīmad Bhāgavata Mahāpurāṇa 2.2.24 — Sanskrit Wikisource (pinned oldid=200166)
'vaishvanaram yati vihayasa gatah sushumnaya brahma-pathena shocisha, vidhuta-kalko 'tha harer udastat prayati cakram nripa shaishumaram' (SB 2.2.24).
