If the soldier in question is a sentry, he could have been armed with anything.
Could be an old match lock, I would be surprised if it were a flintlock as those were very new in 1654 and things were used until they were worn out.
I really doubt it is a wheel lock as those were very expensive and you would not issue something that high guilder to a sentry.
My best guess is an arquebus match lock. That one has an downward hooked butt. In an emergency, I think you turned your arquebus around and used that end as a spiked club.
There were using matchlocks in the English Civil
http://historyonthenet.com/Civil_War/weapons.htm
Some excellent pictures of a military matchlock here
http://www.engerisser.de/Bewaffnung/...s/Caliver.html
http://www.vikingsword.com/vb/showthread.php?t=15432
I can't see the hands well enough to know. Maybe he is adjusting the punk or putting a screw back in.
I just love the Dutch paintings from that period.