According to the opinion of Northern Grammarians after the words with vṛddhi in the first syllable when it is not a gotra -name, the affix phiñ is used in the sense of a descendant.,
Thus आम्रगुप्तायनिः \son of आम्रगुप्त,\ ग्रामरक्षायणिः 'son of ग्रामरक्ष' ॥ नापितायनिः 'son of a barber.' This latter is formed in spite of 4.1.152, because rule (1. 4. 2) applies here.
Why do we say 'according to the opinion of Northern Grammarians'? Observe आम्रगुप्तिः. Why do we say 'after a word having a Vriddhi in the first syllable'? Observe याज्ञदत्तिः 'son of यज्ञदत्त.' Why do we say 'not being a Gotra-name? Observe औपगविः ॥,