अधोलोकवर्णनम् (Adholoka-varṇana) — Description of the Lower Worlds and Cosmographic Measures
तस्माच्च ऋतवो ज्ञेया ऋतुभ्यो ह्यार्त्तवाः स्मृताः / तस्मादृतुमुखी ज्ञेया अमावास्यास्य पर्वणः
tasmācca ṛtavo jñeyā ṛtubhyo hyārttavāḥ smṛtāḥ / tasmādṛtumukhī jñeyā amāvāsyāsya parvaṇaḥ
Therefore the seasons (ṛtu) are to be known, and from the seasons the Ārtavas are remembered. Hence, in the observance (parva) of Amāvāsyā, that called Ṛtumukhī is to be understood.