Pelycosauria

from The Century Dictionary.

• In more recent use, a group, considered by Osborn an order, of reptiles, comprising extinct species having biconcave vertebræ, perforated by the notochord and with very long spinous processes.
• A division of reptiles, containing those Thero-morpka or Theromora which have the coracoid reduced, ribs two-headed, two or three sacral vertebræ, the centra generally notochordal, and intercentra usually present. They lived during the Carboniferous or Permocarboniferous epoch.

from the GNU version of the Collaborative International Dictionary of English.

• proper noun An order of extinct reptiles including edaphosaurus and dimetrodon.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun edaphosaurus; dimetrodon