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On Amphicaiias, a genus of Sauriaris from the Dakota epoch of Colorado. 

 By E. D. Cope. 



The genus to which the above name is now given, is allied to Camara- 

 saurus, of which, and the gigantic species G. supremus, I have given an 

 account in my Paleontological Bulletin, No. 25. Both genera differ from 

 their nearest ally Ornilhopsis Seeley, in the excavation of the vertebral 

 centra, so as to include large chambers separated by a septum, which com- 

 municate with the external median by a lateral foramen. In the Omithop- 

 sis it is stated that the vertebral centra are occupied by a number of coarse 

 cells. In the more remotely allied Cetiosaurus, Owen has observed that 

 the tissue of the centra is coarsely spongy. 



The vertebra from all parts of the column of Camarasaurus are known, 

 and those of the dorsal and lumbar regions present the extraordinary char- 

 acter, of which a trace is seen in Cetiosaurus, of neural spines expanded 

 transversely to the axis of the column. Numerous vetebra of AiwpMcce- 

 lias are known, and in the dorsals in which the neural spine is preserved, 

 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 amphiwelous, the posterior extremitj^ being 

 more concave, and with concave prominent margins ; while the opposite 

 one is less expanded and is but slightly concave. The neural arch is 

 coossifieel 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 Camarcosaitrus, 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 supero-lateral 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 hyposphen, as the inferior reversed wedge may be 

 termed, 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, audit 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- 



