Bull 551, S.2864 -

Charles I (1625-49), Halfcrown,York Mint, (1643-4) Type 2, King seated on horseback left, with grass ground-line below mm. lion, CAROLVS. D. G. MAG. BRI. FR. ET. HI. REX., rev., oval garnished shield CHRISTO.AVSPICE. REGNO., mm Lion (Bull 55 1 ; Besly I-B; Brooker 1077, Hawkins 2; N.23 1 0; S.2864). Weight 14.08 grams.

The reverse has been struck from a rusted die. It's worth noting the different style displayed on these early issue York Halfcrowns compared to the later issued types. 

Provenance: Ex Dunham Collection

Images courtesy of M&H coins, and taken from M&H circular III which features York halfcrowns from the collection of Maurice Bull