I came across the following observations in a web page and thought I will just share this new knowledge (to me) with our members:
Svayambhuva-Manu married Shatarupa, who bore him three daughters by name Akuti, Devahuti and Prasuti. Of these Akuti was given in marriage to the Prajapati Ruchi who had through her a son and a daughter. The son was no other than Hari known by the title 'Yajusham-pati' i.e. lord of the Yajus (mantras) (Bhag. 4-1-6) and the daughter was called Dakshina. Hari as 'lord of the Yajus' was called Yajñadeva whose consort was Dakshini. She was believed to be an amsa (aspect) of Bhuti i.e. Lakshmi. The brother and sister were married as husband and wife. To these were born twelve sons who were collectively called Yama-Devas. Their names were Tosha, Pratosha, Samtosha, Bhadra, Shanti, Idaspati, Idhma, Kavi, Vibhu, Vahni, Sudeva and Rochana....
Marriage of paternal cousins, now condemned, is not unknown to Hindu tradition. Marichi and Daksha were brothers and Kasyapa, the son of the former, married Aditi and other daughters of the latter. These instances seem to bring the early Hindu marriage system into a line with the Egyptian system and suggest that the present Muhammadan custom of marrying paternal cousin sisters was not unknown to the ancient Hindus as to the Egyptians. Aegyptus, the son of Belus, gave his fifty sons in marriage to the fifty daughters of his brother Danaus
Reference: A post in tamilbrahmins page