The words paricāyyaḥ , pacāyya and samūhyāḥ are irregularly formed when they are names of fire.,
These words are thus formed:- परि + चि +ण्यत् = परि + चै + य = परि + चाय + य = परिचाय्यः 'sacrificial fire arranged in a circle' (the ऐ being changed into आय् by the analogy of (VI. I. 79). This peculiar sandhi before the semivowel य has been illustrated in the previous examples also). So also उपचाय्यः 'a kind of Sacred fire'. सम् + वह + ण्यत् = सम् + ऊह् + य = समूह्यः 'a kind of fire'. समूह्यं चिन्वीत पशुकामः 'let him kindle the Samuhya fire desirous of a victim'.
Why do we say 'when they are names of fire'? Observe otherwise, परिचेयम् 'to be heaped', उपचेयम् 'to be increased', संवाह्यम् 'to be carried'.,