The H I structure and kinematics of the peculiar starburst galaxy NGC 3310
(Arp 217, UGC 5786) are discussed. New evidence bearing on the origin of th
e starburst is presented. The bulk of H I coincides with the bright optical
disk and shows differential rotation. Its velocity dispersion is, however,
unusually large for a spiral galaxy (up to similar or equal to 40 km s(-1)
), suggesting that the disk is highly perturbed as already indicated by opt
ical emission line spectroscopy. There are, in addition, two prominent H I
tails, one extending to the north-west and the other, somewhat patchy, to t
he south. These H I tails, the perturbed kinematics and the peculiar optica
l morphology strongly suggest a recent merger between two gas-rich galaxies
. This seems to have been a major merger in which most of the gas in the in
ner parts has been preserved in neutral atomic form and either one of the p
rogenitor disks has survived or a new disk has formed.