Arkell.1956.Jurassic..

WESTERN INTERIOR OF THE UNITED STATES 549
C. (S.) schucherti most resembles C. (S.) mirabile Arkell (Mariae Zone).
C. (C.) lilloetense seems to belong to the group of C. persecans Buckman
(Cordatum Zone). The Vertebriceras are most like Cordatum Zone
forms; C. (V.) stantoni is close to C. (V.) gracile Arkell. I have not
attempted to subdivide the Goliathiceras, but at least G. russelli and perhaps
several others are probably Pachycardioceras, as Imlay suggests.
It is curious that other families of ammonites are almost absent
(see however, Imlay, 1947, pp. 260-1). In other regions, especially
England and Europe, they abound at every level represented by these
Cardioceratids.
Elsewhere some elements of these faunas have been found in the
basal Curtis formation of the Uinta Mountains in Utah and Colorado,
and in Yellowstone National Park, etc. (Imlay, 1952, pp. 964-5; 1947,
pp. 260-1; Crickmay, 1936).
LOWER CALLOVIAN
In the lower part of the Sundance formation in the Black Hills and
Wyoming, and in the equivalents in Utah, Arcticoceras henryi (Meek &
Hayden) is common, with Arcticoceras spp. and many pelecypods. In the
Wind River Basin, Wyoming, the Arcticoceras beds are succeeded by beds
with Gowericeras spp. In the Rierdon formation of Montana these two
zones occur with Kepplerites (Seymourites) beds above, and beds with
Arctocephalites below. The following six zones have been made out in
this and other Rocky Mountain states, and the ammonites have been well
figured (Imlay, 1948, 1953);
TOP
Zone of Seymourites mclearni Imlay, with Kosmoceras, Grossouvria
and Macrocephalitids
Zone of Seymourites tychonis (Ravn), with Cadoceras spp.
Zone of Gowericeras subitum Imlay, with Cadoceras spp., Xenocephalites
shoshonense (Imlay) and rare Perisphinctids
Zone of Gowericeras costidensum
Zone of Arcticoceras codyense, with Cadoceras and small Arctocephalites
Zone of Arctocephalites spp.
The exact correlation of these zones with those recognized in Europe
presents many difficulties. It has been fully discussed by Imlay (1948,
1953), who has been able by the use of these zones to make widespread
correlations through the Western Interior states (1952). The occurrence
of Macrocephalitids at the top agrees with Canada and has its counterpart
in England, though there they are commoner below; and the absence of
Macrocephalitids at the bottom agrees with Greenland. Kosmoceras
at the top and Gowericeras in the middle of the Lower Callovian also
agrees with England; and the presence of Xenocephalites in the Gowericeras
zones, since it- occurs with Reineckeiae in South America, further indicates
that these zones cannot be low in the Lower Callovian. The Arcticoceras
and Arctocephalites zones (and also Crancephalites of Greenland) are all
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