Agnipurana 336.24

336.24

kulakaṃ muktakaṃ koṣa iti padyakuṭumbakam /
sargabandho mahākāvyamārabdhaṃ saṃskṛtena yat //

kulaka, muktaka, and koṣa: this is the family of metrical poetry.
A mahākāvya is composed in cantos, begun in Sanskrit;