In a bahuvrīhi samāsa the word karṇa standing as second member has acute accent (udātta) on the first syllable when it is preceded by a word denoting colour or mark.,
Thus with color we have शुक्लक꣡र्णः, कृष्णक꣡र्ण, and with mark-name, we have दात्राक꣡र्णः शङ्कूक꣡र्णः, the lengthening of दात्र and शंकु takes place by 6.3.115. The marks of 'scythe', 'arrow' &c, are made on the ears of cattle to mark and distinguish them. It is such a 'mark' which is meant here, therefore, the rule does not apply to स्थूलकर्णः ॥ Why do we say कर्ण? Observe श्वेतपादः, कूटशृङ्गः here श्वेत being formed by अच् (II. I. 134) is end-acute, and कूट being formed by क (III. I. 135) is also end-acute and these accents are retained in the compound. Why do we say \when preceded by a word denoting color or mark\? Observe शोभनपादः where शोभन being formed by युच् 2.2.149 is end-acute and this accent is retained 6.2.1.,