SB 12.7.16

rājñāṁ brahma-prasūtānāṁ
 vaṁśas trai-kāliko ’nvayaḥ
vaṁśānucaritaṁ teṣāṁ
 vṛttaṁ vaṁśa-dharās ca ye
Synonyms: 
rājñām — of the kings; brahma-prasūtānām — born originally from Brahmā; vaṁśaḥ — dynasty; trai-kālikaḥ — extending into the three phases of time (past, present and future); anvayaḥ — the series; vaṁśa-anucaritam — histories of the dynasties; teṣām — of these dynasties; vṛttam — the activities; vaṁśa-dharāḥ — the prominent members of the dynasties; ca — and; ye — which.
Translation: 
Dynasties are lines of kings originating with Lord Brahmā and extending continuously through past, present and future. The accounts of such dynasties, especially of their most prominent members, constitute the subject of dynastic history.