GONIATITES, -ti'tez ( Neo-Lat., for *Gonialites, from Gk. yovia, !Ionia, angle Mos, lithos. stone, in allusion to the angulate sutures). An extinct tetrabranchiate cephalopod, the shell of which resembles that of the Ammonoidea in form. but differs from it in having a simple suture line that shows undulating or zigzag curves without secondary crimping. The Gonia tites have smooth unornamented shells of discoid or globular form, with open or closed umbilicus. They vary in size from 1 to 4 inches, though some species from the Devonian system attain a diameter of over 12 inches. The name Gonia tites has long been used in a generic sense; but the group has proved to be heterogeneous, and the species have been redistributed among a number of new genera and four new suborders, the Microcampyli, Mesocampyli, Eurycampyli, and Glossocampyli, these names referring to the form of the saddles of the sutures in the types of the different groups. The old genus Gonia
tites was considered to be an intermediate form between the Nautiloidea and the Ammonoidea, and the above-mentioned suborders represent, in a broad way, transition groiips between certain races of nautiloids and certain races of am monoids.
The species of Goniatites appear first in the lowest Devonian rocks, and they disappear in the Triassic system; their period of maximum development was during Upper Devonian and Lower Carboniferous time. They are thus index fossils of the Upper Paleozoic age. They are found in Europe, Asia, Australia, and North America, often in such abundance that the beds containing them have received the names of Cly merien-kalk and Goniatites limestone. See Am MONOIDEA and CEPIIALOPODA, and the bibliography given under the latter title.