Diagnosis:
The centrum of the vertebrae is very short, but the diameter is
relatively large. Posterior to the diapophyses, the centrum is
greatly constricted, 1.2 mm in diameter, whereas at the anterior
end it measures 4 mm, and at the posterior end 3 mm. The diapophyses and parapophyses for rib articulation arise near the
middle of the bone, and are directed outward and backwards. The
two are joined together almost to their distal points by a weblike
bony connection, the combined width at the tip being 2.8 mm.
The length of the centrum is 5 mm. The notochordal perforation is about 0.5 mm in diameter. Within the notocoele there is a
distinct offset as if a second tube were inserted in the middle of
the centrum, the edges forming the offset. The prezygapophyses
have large articular surfaces. The terminal neuropophysis is large
and broad, bearing a small spearlike elevation that is flattened
against the ventral surface and pointed backward. Two small
openings occur in the tip of the neuropophysis. The elevation of
the vertebra is 7 mm above the base of the centrum. The dorsal
surface of the arch has a very slight keel.
Fossil History:
Known only from the type locality. The Rhinoceros Hill deposit, as interpreted by Elias (1931, p. 161) lies 50 to 80 feet higher than the "Edson beds", at the type locality of Ambystoma kansense.