Trocholitidae Chapman 1857

Family Trocholitidae Chapman, 1857 Diagnosis (after Furnish & Glenister 1964; Frey 1995; emended) Family of the order Tarphyceratida with subglobular to discoidal conchs consisting of three to five or more gradually expanding volutions; body chamber may uncoil from preceding volution. Terminal aperture of body chamber with flares in some taxa, aperture often modified with ventral sinus and lateral projections. Whorl profile usually impressed dorsally; usually depressed except for the adult growth stage that may have an equidimensional or compressed whorl profile; flanks and venter broadly rounded or flattened. Shell ornament varies during ontogeny, usually consisting of imbricating and / or frilled lirae, ribs or annuli, but taxa with smooth shell surface exist; ornament elements form ventral sinus. Conch in some taxa with periodic constrictions. Phragmocone chambers short (on average six phragmocone chambers relative to whorl height). Suture line simple with shallow ventral lobe or rarely saddle. Siphuncle subcentral, subdorsal or marginodorsal in position, ventral to central in initial volution; siphuncle segments tubular, weakly convex or weakly concavo-convex, narrow in diameter (usually less than 0.25 of apertural height); septal necks short (less than 0.20 of segment length), orthochoanitic or loxochoanitic; connecting rings usually thick, layered, but becoming thin and homogeneous in some taxa. Genera included Arkoceras Ulrich, Foerste, Miller & Furnish, 1942; Crenuloceras Flower, 1968; Curtoceras Ulrich, Foerste, Miller & Furnish 1942; Discoceras Barrande, 1867; Hardmanoceras Teichert & Glenister, 1952; Jasperoceras Ulrich, Foerste, Miller & Furnish, 1942; Litoceras Hyatt, 1884; Paradiscoceras Barskov, 1972; Plectolites Flower, 1968; Trocholites Conrad, 1838; Trocholitoceras Hyatt, 1894; Weberoceras Barskov, 1972; Wichitoceras Ulrich, Foerste, Miller & Furnish, 1942; Yushanoceras Chen & Liu, 1976. Remarks Chapman (1857) must be regarded as the correct author of the family name. Trocholitidae Schröder, 1891 is an objective junior synonym. The diagnosis compiled from Furnish & Glenister (1964) and Frey (1995) is rephrased and modified to reflect results of the revision of Trocholites and Curtoceras performed herein. The added details concern the shape of the terminal aperture, whorl profile, shape of connecting rings and shape of septal necks.