Pisiform is which type of bone:
Pneumatic bone
Sesamoid bone
Accessory bone
Long bone
The pisiform is a sesamoid bone, with no covering membrane of periosteum. It is the last carpal bone to ossify. 
The pisiform bone is a small bone found in the proximal row of the wrist (carpus). 
It is situated where the ulna joins the wrist, within the tendon of the flexor carpi ulnaris muscle.