Compare the pictorial approach to its narrative equivalent below (salient features in color):
|Introduction: Small trilobites
(usually only a few mm long) with cephalon and pygidium
strongly similar in outline and size (isopygous); enrollment typical.
Cephalon: cephalic shield with deeply parabolic outline, maximum width usually anterior of genal angle, sutures proparian or lacking; border convex; glabella fusiform, widest at base (except in Condylopygidae), glabellar segmentation highly variable, sometimes complex, but in some species entirely effaced; most species eyeless; hypostome natant, sometimes specialized with ribbon-like wings; rostral plate lacking (or uncalcified).
Thorax: segments 2 (Agnostina) or 3 (some Eodiscina), axis typically broad, short fulcrate pleurae.
Pygidium: strongly isopygous; pygidial margin typically closely matching cephalic margin.
Occurrence: L. Cambrian to U. Ordovician (Ashgill).
AGNOSTIDA includes two Suborders:
Walking Trilobite animation ©2000 by S. M. Gon III