Tower mint crown, group 1b, mm castle 1627-8:
Obverse: (castle) CAROLVS D'.G'.MAG'.BRI'.FRA'.ET HIB'.REX - Charles by the grace of God King of Great Britain France and Ireland. First horseman, type 1b, king on horseback left, horse caparisoned with plume on head and crupper.
Reverse: .CHRISTO.AVSPICE.REGNO.(castle) - I reign under the auspices of Christ. Square-topped shield, plume above.
Weight: 29.9 grams. Diameter: 43 mm.
Ex - Cooper lot 53, Larsen lot 144, Hall, Alan Barr lot 390.
Castle is the rarest mint mark in the Tower series.
Much better than photo suggests.

Sold June 2014