THE PERICYCLIDAE are distinctive ancestral (middle Tournai-
 sian-lower Viséan) Goniatitina characterized by prominent
 transverse sculpture.  Ancestry of the group was in Goniocyclus
 Gordon, 1986 (type species, Goniatites blairi Miller and Gurley,
 1896).  These diminutive (generally less than 35 mm), coarsely
 ribbed pericyclids are distinguished by sharply angular ventral
 sinuses and sutures with primitive, incipiently bifid ventral lobes.
 Goniocyclus characterizes the late Kinderhookian (late middle
 Tournaisian) Siphonodella isosticha-Upper Siphonodella cren-
 ulata conodont Zone where it is represented by at least six dis-
 tinctive species in the North American Cordillera and Midconti-
 nent (Gordon, 1986).  The earliest record, which extends the ge-
 neric range back to the base of the traditional middle Tournaisian,
 is a widely discussed, but previously undescribed, species from
 the Hannibal Shale of Missouri (Work et al., 1988; Becker, 1993a,
 1993b; Popov and Kusina, 1997) described herein as
 Goniocyclus hannibalensis new species.