The Locative -7th case-affix ending is optionally retained after the words 1. śaya 2. vāsa and 3. vāsin when the preceding word does not denote time and ends in a consonant or a short a,
Thus खेशयः, or खशयः, ग्रामेवासः or ग्रामवासः, ग्रामेवासिन् or ग्रामवासिन् ॥ After a time-name we have पुर्वाह्णशयः ॥ After a vowel ending word (other than अ) we have भूमिशयः ॥
Vart:- The Locative case-affix is retained after अप् when योनि, or the affix यत् or मतुप् follows. Thus अप्सुयोनिः, अप्सव्यः, अप्सुमन्तौ ॥ The affix यत् is added by treating अप् as belonging to the दिवादि class (अप्सु भवः, 4.3.54).,