But is that all ?

The confusing fact is that, according to Snell's Neuroanatomy (5th ed./p.316):
"The Subthalamic nuclei, the Substantia nigra & the red nucleus are functionally closely related to the basal nuclei, but they should not be included with them."

Whereas, Guyton (10th ed./p.656) considers the Subthalamic nuclei & the Substantia nigra part of the basal ganglia; although they do not mention anything about Claustrum.

Again, according to Snell's Neuroanatomy (5th ed./p.319):
"The function of the claustrum is unknown."

Bad, very bad.