Samjna, daughter of Vishvakarma, shuts her eyes before the Sun, who in anger foretells that she will bear Yama and a restless river. Unable to bear the heat she tells her shadow to stay in her place and keep silent short of being seized by the hair or cursed. Her father sends her back; she goes instead to the Northern Kurus as a mare and fasts. The shadow bears Savarni, Saturn and Tapati and favours them. Yama lifts his foot against her and she curses it to fall; the Sun softens this to worms carrying a little flesh away, and threatens the shadow until she confesses. Vishvakarma mounts the Sun on his wheel (in Shakadvipa) and pares away fifteen sixteenths while the worlds reel and the gods sing; from the parings he makes Vishnu's discus, Shiva's trident, Kubera's palanquin, Yama's rod and the war god's spear. The Sun goes north as a horse; from the meeting of their noses the Ashvins are born, and then Revanta. She comes home.
Two verses at the head of a funeral hymn. Tvashtri holds a wedding for his daughter and all the world assembles; the mother of Yama, wife of great Vivasvat, vanishes as she is led to her home. 'They' hide the immortal woman from mortals, make one like her and give that one to Vivasvat. Saranyu bears the two Ashvins and leaves two pairs of twins. Nothing else is said.
What is different here:
The bride is Saranyu and her father Tvashtri. Unnamed others make the double. No reason, no heat, no curse, no lathe, no return.
Tvashtri has twins, Saranyu and the three-headed Trishiras, and gives Saranyu to Vivasvat. She bears the twins Yama and Yami. In her husband's absence she makes a female like herself, entrusts the pair of children to her, turns into a mare and departs. Vivasvat, unaware, begets Manu on the substitute. Learning the truth he follows as a horse; she recognises him; the twins Nasatya and Dasra, the Ashvins, are born. The account ends there and refers to Yaska.
What is different here:
Saranyu makes the double herself. Manu is the substitute's son. No shadow, no heat given as the reason, no curse on Yama, no lathe, no homecoming.
A single paragraph. Samjna, daughter of Vishvakarma, bears Manu, Yama and Yami, gives the Sun her shadow Chhaya as handmaid and goes to the forest. Chhaya bears Shani, Savarni Manu and Tapati. Offended with Yama she curses him, which reveals that she is not his mother. The Sun sees Samjna in meditation as a mare in Uttara Kuru, joins her as a horse and begets the Ashvins and Revanta, and brings her home. Then Vishvakarma grinds off an eighth of his radiance on the lathe and makes the discus of Vishnu, the trident of Shiva, Kubera's weapon and Kartikeya's lance from it.
What is different here:
Only an eighth is ground away (not fifteen sixteenths) and the lathe comes after the homecoming, not before. No dialogue.
The Sun's wife is called Rajni, the same as Dyaus, born as Samjna or Sarenu to the wife of Vishvakarma. The Sun takes a human form to wed her; she bears Manu, Yama and a daughter. The story of her penance in the Northern Kuru country and of the lathe is told to glorify the Sun; the lathe is set in Shakadvipa, and an image carved afterwards by Vishvakarma is the one Samba later finds in the Chandrabhaga.
What is different here:
Renames the wife Rajni and ties the lathe episode to the Sun-image of Mitravana.
Sources: The Markandeya Purana, tr. F. E. Pargiter (Bibliotheca Indica, 1904); Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer; The Brhad-devata attributed to Saunaka, ed. and tr. A. A. Macdonell (Harvard Oriental Series 6); The Vishnu Purana, tr. H. H. Wilson (1840); Studies in the Upapuranas, vol. 1: Saura and Vaisnava Upapuranas, R. C. Hazra (Calcutta, 1958)