The affix yat comes in the sense of 'who sleeps' after the word samānodara in the Locative -7th case construction and the udātta falls on the letter o,
The word शयित is equal to स्थितः 'remain'. Thus समानोदरे शयितः = समानोदर्यः 'uterine brother' i. e. who has slept in the same womb. See 6.3.88.,