Phylum: Arthropoda
Class: Trilobita
Order: Asaphida
Family: Asaphidae (Burmeister, 1843)
Cincinnatian Genus: Isotelus

Geologic Range
Late Cambrian – Late Ordovician

Common Paleoecology
Asaphidae is an extinct family of fast-moving low-level epifaunal deposit feeders.

Description of the Family

  • Glabella longer than frontal area.
  • Glabellar furrows weak to absent.
  • Doublure commonly broad.
  • 8 segments in thorax.
  • Pygidium rounded to pointed.

Published Descriptions

Treatise on Invertebrate Paleontology, Part O (1959):

  • Librigenae separated anteriorly by a median suture; glabella well defined to obsolete, considerably longer than frontal area; lateral glabellar furrows mostly weak or absent; most genera with distinct glabellar tubercle; eyes generally somewhat distant from axial furrows; faint, almost obsolete eye ridges known only in 2 genera. Doublure commonly broad; posterior margin of hypostoma varying from pointed to deeply notched. Thorax of 8 segments; pleural furrows generally diagonal, if present. Panderian organs developed as notches or separate openings, but absent in some (Ogygiocaridinae, Symphysurininae). External margin of pygidium varying from rounded to pointed, in some genera with terminal spine; paired pygidial spines present in single genus of uncertain affinities. Dorsal surface of carapace with small pits, terrace lines, or both; no tuberculate or granulose ornamentation. Family tends toward loss of apparent segmentation of cephalon and pygidium, obsolescence of axial furrows, and deep notching of posterior margin of hypostoma.