76 Saurians of the Dakota Beds of Colorado, | February, 
hand the bones of the tail and limbs are solid or nearly so,in 
great contrast with some of the Dinosauria of later geological | 
periods. E 
The manner of the mutual articulation of the arches of the l 
vertebræ in the genera Camarasaurus and Amphicelias is very 
peculiar, and has not been observed in any other animals. 
The anterior zygapophyses are separated by a deep fissure, l 
while the posterior zygapophyses are united on the middle line. 
From the latter from the point of junction, there descends a ver- 
tical 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 
zygapophyses above, and the Ayposphen, as I have termed the in- 
ferior reverse wedge, below. This arrangement accomplishes the 
purpose effected by the zygosphenal articulation, that is the 
strengthening of the articulation between the neural arches, but in 
a different way. The additional articulation is placed at the opposite 
extremity of the vertebre, and it is the anterior zygapophysis in- 
stead of the posterior one which is embraced. This structure enti- 
tles the genera which possess it to family rank, and as the two 
genera mentioned above belong to different families in conse- 
quence of the different types of vertebral centra, the one opis- 
thoccelous, the other amphiccelous, they have been called Camara- 
sauride and Amphicelide respectively. 
This structure is readily seen by reference to Figs. 5 and 13, 
where it is represented in the vertebrae of the two genera from 
behind. In Fig. 2 it is replaced by a stouter vertical plate of 
bone, which spreads out a little below. It is seen in profile in 
ig. 3. It is not present in the vertebre of the tail. 
-© The characters of the genus Camarasaurus are derived from 
nearly all portions of the skeleton excepting the skull and 
ungues. The bones are generally in good preservation. 
The vertebrze of the cervical, dorsal and lumbar region are all 
opisthoccelous or reversed ball and socket. The centra of the — 
cervicals are very elongate, but those which follow them diminish — - 
_ rapidly in length, until in the lumbar region they have but asmall 
= anteroposterior diameter, The anterior caudal vertebra are also 
