The affix ya comes in the sense of 'who sleeps' after the word sodara the word being in the Locative -7th case in construction.,
By sutra 6.3.88 समान is optionally changed to स before the word उदर when यत् follows. Thus समानोदरे शयितः = सोर्द॒॒यः꣡ ॥ Here ओ is not udatta, as it was in the last; the udatta here falls on य ॥,