Discoceras Barrande 1867

Genus Discoceras Barrande, 1867 Type species Clymenia antiquissima Eichwald, 1842; by subsequent designation (Schröder 1891). Diagnosis (after Kröger & Aubrechtová 2018; Manda & Turek 2018) Genus of the family Trocholitidae with adult conch diameters between 40 and 150 mm or more; body chamber usually divergent from preceding whorl, aperture may be slightly constricted or ventrally flared; whorl profile weakly depressed, equidimensional or weakly compressed; shape of whorl profile circular, elliptic, subquadrate, trapezoidal or heart-shaped; whorls weakly embracing or not embracing; caecum subcentral, shifted towards ventral side, siphuncle shifts dorsally in second and third chamber, final dorsal or subdorsal position is attained in third septum; thick, layered connecting rings; shell surface smooth or ornamented with frilled and imbricated to lamellar lirae, narrow to strong annuli or ribs present in some taxa; ornament forms ventral sinus. Remarks Among the Ordovician Baltoscandian trocholitids, the genera most similar to Discoceras are Curtoceras Ulrich, Foerste, Miller & Furnish 1942 and Trocholites Conrad, 1838 (see Aubrechtová & Korn 2025 for detailed discussions). The species of both genera are smaller in adult diameters (usually between 20 and 60 mm), and their shells are more finely ornamented; the ornamentation elements are neither frilled nor strongly imbricated. In Curtoceras, the whorl profile is equidimensional or nearly so, with convex or only slightly flattened ventral and lateral sides. In Trocholites, the conch is stouter, more tightly coiled, the whorls embrace each other and the whorl profile is much more depressed. In Discoceras, the adult conch size usually exceeds 100 mm, and the shell is ornamented with frilled and imbricated elements. The terminal body chamber is typically uncoiled to varying degrees. The adult growth stages of Discoceras are extremely discoidal (CWI