14 
Donald Baird and John R. Horner 
missing), which Cope took to be the shaft of the left tibia, appears instead 
to be part of a carnosaurian left femur. 
Material acquired since 1869 adds little to the morphological informa- 
tion provided by the lectotype vertebra. The largest and presumably most 
anterior vertebra (ANSP 15338) is slightly longer than its centrum height, 
and the more posterior vertebrae become increasingly elongate, exactly as 
illustrated by Gilmore in the tail of Parrosaurus. The ends of the centra are 
hexagonal, wider than their height, and slightly amphicoelous (nearly 
amphiplatyan) with chamfered rims. In well-preserved specimens the up- 
per third of the end surface is rugose, typically showing a semi-sunburst 
pattern that centers on the neural canal. In lateral view the centra are 
marked by low, rounded, longitudinal ridges at mid-height; there are no 
pleurocoeles. Ventrally the centrum is excavated by a broad, moderately 
deep, boat-shaped sulcus which is bounded laterally by rounded ridges 
that connect the anterior and posterior facets for the haemal chevrons. 
The neural arch is centered at mid-length on the centrum and is com- 
pletely co-ossified with it, so that only a difference in the orientation of 
surface striae reveals the position of the neurocentral suture. The anterior 
zygapophyses are short, terminating well behind the anterior margin of 
the centrum; their articulating facets are inclined about 30° from the ver- 
tical. The neural spine (only the base of which is preserved) arises from 
the posterior half of the arch at a low angle (22° in the type); its base is 
broadly ogival in cross-section. An experimental reconstruction in clay 
shows us that the spine must have projected at least half a centrum length 
behind its vertebra in order to articulate with the zygapophyses of the 
next succeeding vertebra. Of course we cannot say whether the spine 
maintained its initial angle or whether it became more bladelike distally. 
The smallest vertebra is a topotypic specimen, now missing, illustrated 
by Cope (1875, PI. 5, Figs. 2-2a-2b) as possibly belonging to a young in- 
dividual of Hadrosaurus tripos. (In Cope’s plate, oddly, it is shown with the 
lateral and end views upside down and the dorsal view captioned 
“below.”) Its centrum height is given as 20.5 lines, i.e. 43.4 mm; height at 
end, 38.1 mm; width of end, 45.1 mm; width of waist, 31.8 mm. In 
morphology this centrum falls well within the range of variation of the 
Hypsibema caudals from Phoebus Landing. Its small size and lack of co- 
ossification with the neural arch indicate immaturity. Centrum dimen- 
sions of some larger vertebrae are shown in Table 1. 
The genus Parrosaurus. — A sequence of 13 caudal centra (USNM 16735) 
recovered by well-diggers on the Chronister farm near Glen Allen, 
Bollinger County, Missouri, was described by Gilmore as a new genus 
and species, Neosaurus (later renamed Parrosaurus) missounensis. The source 
