NL400 facing a weird river bet

[tompss]

ongame NLHE400 I have played only a couple of hands on this table and haven't played with villain before.

Seat 1: Hero ($435.80 in chips)
Seat 3: SB ($50.30 in chips)
Seat 6: Villain ($1,213.60 in chips)
Seat 10: UTG ($964 in chips)

ANTES/BLINDS
SB posts blind ($2), Villain posts blind ($4).
Hero 9[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/club.gif[/img]
PRE-FLOP
UTG folds, Hero bets $15, SB folds, Villain calls $11.

FLOP [board cards: 6[img]/images/graemlins/spade.gif[/img] J[img]/images/graemlins/diamond.gif[/img] 6[img]/images/graemlins/club.gif[/img] ]
Villain checks, Hero checks.

TURN 7[img]/images/graemlins/spade.gif[/img]
Villain checks, Hero bets $24, Villain calls $24.

RIVER 5[img]/images/graemlins/heart.gif[/img]
Villain bets $75, Hero ?