ṣ is substituted for the s when followed by e and preceded by iṇ or ku , when the word is a name and when the s is not preceded by g,
Thus हरयः सेना अस्य = हरिषेणः, परितः सेना अस्य = परिषेणः, so also वारिषेणः, जानुषेणी ॥ Why do we say 'followed by ए'? Observe हरिसक्थम् ॥ Why do we say 'when a Name'? Observe पृथ्वी सेना यस्य स = पृथुसेनो राजा 6.3.34. Why do we say 'when the स is not preceded by ग्'? Observe विष्वक् सेनः ॥ The phrase इण्कोः is understood here also, so the rule does not apply to सर्वसेनः ॥,