After a word being in construction in the Locative -7th case, an affix (one of those ordained already) comes in the sense of 'generally found therein'.,
The word प्रायः means something less than all i. e. abundant. Thus स्रौघ्नः 'what is abundant or mostly to be found in Srughna', = स्रुघ्ने प्रायेण बाहुल्येन भवति. So also माथुरः, राष्ट्रियः &c.
This sutra may appear to be superfluous as being covered by the more comprehensive sutra तत्रभवः 4.3.53. If प्रायभवः be explained as अनित्यभवः i. e. what sometimes is to be found and sometimes not, still it will make little difference.,