Matsya Purana — The Attendant Hosts of the Sun and Moon: Monthly Gaṇas
अर्धमाससमाप्तौ तु पीत्वा गच्छन्ति ते ऽमृतम् सौम्या बर्हिषदश्चैव अग्निष्वात्ताश्च ये स्मृताः //
ardhamāsasamāptau tu pītvā gacchanti te 'mṛtam saumyā barhiṣadaścaiva agniṣvāttāśca ye smṛtāḥ //
At the close of the half-month, having drunk the oblation, they depart unto immortality—namely the Saumya Pitṛs, the Barhiṣads, and those remembered as the Agniṣvāttas.
This verse is not about Pralaya; it explains post-death ritual cosmology—how specific classes of Pitṛs, after receiving the offering, proceed toward an imperishable (amṛta) state.
It supports the gṛhastha-duty of performing timely Śrāddha and ancestral offerings: when done in the proper tithi-cycle (fortnightly timing implied), the oblation reaches the Pitṛs and is said to aid their onward state.
The significance is ritual rather than architectural: it emphasizes correct calendrical timing (end of the half-month) and identifies the recipient lineages of Pitṛs (Saumya, Barhiṣad, Agniṣvātta) relevant to Śrāddha procedure.