E. Kruggel & G. Gerbasevskis. Die Munzen des Herzogtums Kurland. 2000. Coins of the Duchy of Courland.

The best study of the coins of the Duchy of Courland. Professional, very detailed catalog of types and varieties of all coins minted from 1578 to 1780.
Riga 2000 dimensions: 177x248 mm, pages: 222, hardcover, German language, new.

Courland / Kurland, Jacob Kettler 1642-1680. Schilling no date, Mitau mint, Kopicki 4051 (R7), Gerb/Krug. 3.2.1.1, Haljak 1697, Billon 16 mm, weight 0,48 g., Condition NGC MS 63, rare type of coin in beautiful condition, centrally weakly struck, surface with nice mint shine

Courland / Kurland. Friedrich Kettler 1587-1642. 3 Groschen (Dreigröscher) 1598, Mitau, Kopicki 4042 R4, Iger KuW.98.1.c R2, Silver 21 mm, weight ca. 2,3 g., Condition PCGS MS 63, nice golden patina on obverse, sharp relief details, mint state - shiny specimen, rare in this state of preservation
Variety with title ending CVR, digits date 98, unseparated and close together.
Aw: MONE . A - RG . CV. R (CVR mistakenly separated by a dot) / Rw: III / GROS . AR . TR / DVCVM CV / . ET . SE . / . 98 .