 Stegosaurus duplex , meaning " two plexus roof lizard " ( in allusion to the greatly enlarged neural canal of the sacrum which Marsh characterized as a " posterior brain case " ) , was named by Marsh in 1887 ( including the holotype specimen ) . The disarticulated bones were actually collected in 1879 by Edward Ashley at Como Bluff . Marsh initially distinguished it from S. ungulatus based on the fact that each sacral ( hip ) vertebra bore its own rib , which he claimed was unlike the anatomy of S. ungulatus ; however , the sacrum of S. ungulatus had not actually been discovered . Marsh also suggested that S. duplex may have lacked armor , since no plates or spikes were found with the specimen , though a single spike may actually have been present nearby , and re @-@ examination of the site maps has shown that the entire specimen was found highly disarticulated and scattered . It is generally considered a synonym of S. ungulatus today , and parts of the specimen were actually incorporated into the Peabody Museum S. ungulatus skeletal mount in 1910 . 
