Cephalon: with opisthoparian sutures; glabella elongate, sides often concave (pestle-shaped), furrows (when not effaced) typically with splayed arrangement, the hind pair pointing sharply backwards, and anterior pairs tending more and more forward directed; sometimes furrows pit-like; cranidial borders often ledgelike; hypostome conterminant or (in derived forms) impendent; eyes typically large, in some gently arcuate.
Thorax: typically with 7-8 segments (but range for order is 2-12, rarely more), pleural tips often spinose.
Pygidium: typically large (isopygous or subisopygous), of variable form, some spinose.
Occurrence: Lower Cambrian – Middle Devonian
Suborders: Corynexochina, Illaenina, Leiostegiina 

Cephalon: with opisthoparian sutures, anterior sutures generally subparallel; glabella long, subparallel, or expanding anteriorly; eyes typically elongate, narrow;  hypostome typically fused with rostral plate (conterminant); genal spines often present.
Thorax: 2-12 (rarely more in primitive genera) segments, pleurae typically spine-tipped.
Pygidium: variable, typically large and spinose, some with smooth border.
Superfamilies/Families: Corynexochoidea: Corynexochidae, Cheiruroididae, Chenghuiidae, Dorypygidae, Ogygopsidae, Oryctocephalidae, Dolichometopidae, Edelsteinaspididae, Jakutidae, Longduiidae, Zacanthoididae, Dinesidae.
Representative Genera: Ogyginus, Dorypyge, Kootenia, Olenoides, Ogygopsis, Oryctocephalus, Bathyuriscus, Hemirhodon, Glossopleura, Orria, Zacanthoides, Dinesus.

Cephalon: typically effaced, opisthoparian facial sutures, but sutures distinctly divergent anteriorly; glabella expands forwards, lateral furrows often faint or absent; hypostome impendent (conterminant, but hypostome no longer matching anterior glabellar border); extra-axial cephalic muscle impression (lunette) present; doublure broad.
Thorax 8-10 segments.
Pygidium: isopygous or subisopygous, rounded posteriorly, usually with short axis.
Superfamily/Families: Illaenoidea/Illaenidae, Phillipsinellidae, Styginidae (=Scutelluidae), Tsinaniidae
Representative Genera: Bumastus, Ectillaenus, Illaenus, Paralejurus, Phillipsinella, Protostygina, Scabriscutellum, Scutellum, Stenopareia.

Cephalon: with opisthoparian sutures; glabella usually subrectangular or quadrate, sometimes broad-based, tapering forward, lateral furrows on glabella often faint or absent; palpebral furrows and eye ridges often present; eyes often medium sized, but variable; genal spines typically present.
Thorax: up to 10 segments.
Pygidium: medium to large, broadly transverse, semicircular, subrectangular, or subtriangular; furrows often faint or absent; axis often persist along nearly full length, sometimes extending into terminal spine, or a pair of lateral spines extending from 1st and 2nd pleural field (Kaolishaniidae)
Superfamily/Family: Leiostegioidea/Leiostegidae, Pagodiidae, Kaolishaniidae, Cheilocephalidae, Lecanopygidae, Shirakiellidae.
Representative Genera: Cheilocephalus, Illaenurus, Kaolishania, Komaspidella, Lecanopyge, Lloydia, Mansuyia, Shirakiella, Szechuanella.