Shiva Purana
तानि चैव तु लक्षाणि सर्वतो वलयाकृति॥ पुष्करद्वीपवलयो मध्येन विभजंति च॥ ६१॥
There is a great ring round it, five hundred thousand Yojanas in length. The Puṣkara Dvīpa ring divides it into two.
english translation
tAni caiva tu lakSANi sarvato valayAkRti॥ puSkaradvIpavalayo madhyena vibhajaMti ca॥ 61॥
hk transliteration by Sanscript