Matsya Purana — Catalogue of the Eighteen Puranas
तदर्थो ऽत्र चतुर्लक्षं संक्षेपेण निवशितः पुराणानि दशाष्टौ च साम्प्रतं तदिहोच्यते //
tadartho 'tra caturlakṣaṃ saṃkṣepeṇa nivaśitaḥ purāṇāni daśāṣṭau ca sāmprataṃ tadihocyate //
Here, the purport of the Purāṇic teaching has been set forth in brief to the measure of four hundred thousand verses. Now, accordingly, the eighteen Purāṇas are stated here.
This verse does not describe pralaya directly; it frames the Purāṇas as a concise, systematized body of teaching (traditionally counted as four lakhs of verses), within which pralaya narratives are included elsewhere.
Indirectly: by identifying the Purāṇas as an organized corpus, it points the reader to the wider Purāṇic guidance on rājadharma and gṛhastha-dharma found in other chapters and Purāṇas.
No specific vāstu or ritual rule is stated in this verse; it functions as a structural marker introducing the authoritative list/teaching of the eighteen Purāṇas, among which vāstu and temple-ritual topics are treated in detail elsewhere.