1877.] ^4d [Cope. 



the latter displays the usual form, that is, it is compressed in the direction 

 of the axis of the column. The centra differ from those of Camarasaurus 

 in the form of their articular extremities, resembling more nearly in this 

 respect the genus Tichosteus Cope (Paleontological Bulletin, No. 26, p. 

 194). They are unequally amphicoelous, the posterior extremity being 

 more concave, and wi^h prominent margins ; while the opposite one is 

 less expanded and is but slightty concave. The neural arch is coossified 

 to the centrum, and there is no capitular costal articulation on the latter. 



The manner of the mutual articulation of the neural arches in this genus 

 is peculiar, and is only paralleled in the genus Camarasaurus, so far as I 

 can ascertain. The anterior zygapophyses are separated by a deep fissure, 

 while the posterior zygapophyses are united on the middle line. From the 

 latter from the point of junction, there descends a vertical plate which 

 rapidly expands laterally, forming a wedge whose base looks downward. 

 The superolateral faces are flat, and articulate with corresponding facets on 

 the inferior side of the anterior zygapophyses, which look downward and 

 inward, on each side of the fissure above described. When in relation, the 

 anterior zygapophyses occupy a position between the posterior zygapophy- 

 ses above, and the hyposph'en, as I have termed the inferior reversed 

 wedge, below. This arrangement accomplishes the purpose effected by the 

 zygosphenal articulation, that is the strengthening of the articulation be- 

 tween the neural arches, but in a different way. The additional articula- 

 tion is placed at the opposite extremity of the vertebra, and it is the anterior 

 zygapophysis instead of the posterior one which is embraced. This struc- 

 ture entitles the genera which possess it to family rank, and as the two 

 genera mentioned above belong to different families in consequence of the 

 different types of vertebral centra, the one opisthoccelous, the other amphi- 

 coelous. they may be called Camarasauridce and AmpMcceliidcB respec- 

 tively. 



The pubis is a stout bone with one slightly concave, thicker border, and 

 an opposite strongly convex, thinner margin. One extremity is truncate ; 

 the other presents one transversely truncate and one oblique face. The 

 femur is elongate, and presents a strong postero-external ridge or third tro- 

 chanter near the middle of the shaft. The head is not separated by a well 

 marked neck, and the great trochanter does not project beyond it. 



Thus while there is a striking resemblance to Camarasaurus in what 

 may be regarded as adaptive characters, in some important essentials the 

 two genera are very different. 



Amphiccelias altus Cope. 



Paleontological Bulletin, No. 27, p. 3. 



The centrum of the dorsal vertebra of this reptile is contracted both lat- 

 erally and inferiorly, so that the margins of the articular extremities flare 

 outwards. The sides are flat, and the inferior surface but little convex in 

 the transverse direction. The pneumatic foramen is situated at the bottom 

 of a large lateral fossa which extends nearly the entire length of the superior 



