The ontogeny of Parabolina spinulosa is described on the basis of material from Andrarum (Skåne) and Jämtland in Sweden. Protaspides are rare, and indifferently preserved, but well-preserved isolated tagmata and complete specimens from the early meraspid stages onwards were available for study. Whereas the ontogeny is broadly similar to that of the earlier Olenus wahlenbergi, there are subtle differences, notably in a greater spinosity from the earlier stages and a gradual, rather than a sudden, change of surface sculpture in the early holaspid. P. spinulosa at all stages of growth is much more variable than is Olenus. Meraspides have larger articulating halfrings anteriorly and the first thoracic segments are of greater sagittal length than in the adult; these were adaptations which enabled Parabolina to undergo cylindrical enrollment from an early stage.

Parabolina is considered to have arisen from the earlier genus Olenus, and on the basis of comparative ontogeny many, though not all, features of Parabolina appear to be of paedomorphic origin. These include the reduction of the preglabellar field, retention of the visual surface, position of the eyes set close to the glabella, retention of a conterminant hypostome, yoking of the librigenae, spinosity of the thorax and pygidium, more numerous glabellar furrows and reduction in number of thoracic segments. Olenus attenuatus has several features intermediate between those of earlier Olenus species and Parabolina, and the origin of the latter genus is best considered in terms of a mosaic paedomorphocline.

The new standard conodont zonation includes, in succession from below: Lower Ps. bicornis Zone, Upper Ps. bicornis Zone, Lower P. procerus Zone, Upper P. procerus Zone, Lower K. ranuliformis Zone, Upper K. ranuliformis Zone, 0. s. rhenana Zone, Lower K. walliseri Zone, Middle K. walliseri Zone, K. patula Zone, uppermost K. walliseri range, post K. walliseri interregnum, K. o. ortus Zone and 0. s. sagitta Zone. Lower boundaries for each zone are defined or redefined. A less detailed biostratigraphic nomenclature at the superzone level is suggested for use where collections are inadequate: The Pterospathodus Zonal group, the Upper Pterospathodus Zonal group, the P. amorphognathoides Zonal group, the Ps. bicornis Superzone, the P. procerus Superzone, the K. ranuliformis Superzone, the O. s. rhenana Superzone, the K. walliseri Zonal group, the Upper K. walliseri Superzone and the K. o. ortus Superzone. These partly overlap and can be used according to the taxa present. The proposed zonation is applied to most known conodont sequences. The taxonomic concept of the taxa used is discussed; new taxa include Nudibelodina sensitiva, Ozarkodina paraconfluens and O. martinssoni. The species name Ozarkodina ortus is a senior synonym of Kockelella absidata.