homocercal

The heterocercal tail of a shark is a caudal fin with unequal lobes.

A heterocercal tail is a caudal fin composed of two asymmetrical lobes.  Often, such as the case in many sharks, the vertebral column passes through the upper lobe, making it the larger of the two lobes.  A heterocercal tail is contrasted with a homocercal tail which has equal lobes.