Arkell.1956.Jurassic..

SWABIAN AND FRANCONIAN ALB 115
The Rasenia trifurcata (Rein.) and R. trimera (Oppel) groups grade
insensibly into Involuticeras Salfeld, of which Schneid (1939, pis. x-xiv)
has figured a number under the wrong name Ringsteadia; there is misleading
homoeomorphy, but comparison with English Upper Oxfordian
Ringsteadia shows that in Schneid's forms the ribbing is much more
regularly fasciculate and the inner whorls are totally different, purely
rasenoid. Similarly, most of Schneid's so-called Pictoniae (1940) are
Raseniae of the Cymodoce Zone.
Subzone of Sutneria platynota (synonym S. reineckiana Quenst. sp.,
proposed as zonal index by Engel, 1883). The boundary between beta
and gamma falls in the middle of this zone, and Beurlen (1926) subdivided
it; Dieterich (1940) calls the lower part (beta) the zone of Sutneria galar
with Taramelliceras falculum. This zone also yields a very rich fauna of
Ataxioceras, Progeronia, Taramelliceras, etc., and from the prevalence of
Prorasenia stephanoides (Oppel) and Pachypictonia Schneid (both of which,
however, range up into the lower part of the Polyplocum Zone) it may best
be correlated with the Cymodoce and Baylei Zones of NW. Europe;
those being in any case only reduced and incomplete representatives.
The Amoeboceras of this zone are A. lineatum (Quenst.), A. bauhini
(Oppel), A. kapfi (Oppel), A. kitchini (Salf.), A. fraasi (Fischer) and A.
cricki (Salf.). Several of these Amoeboceras occur in the Cymodoce
Zone of Market Rasen.
UPPER OXFORDIAN
Zone of Epipeltoceras bimammatum. As with the Tenuilobatus Zone,
the zonal index has since been found to be not good for the whole zone;
it is in fact restricted to the lower part and to the top of what was formerly
included on lithological grounds in the underlying Alternans Zone (the
fossil-beds of Lochen cutting) (Dieterich, 1940).
Subzone of Idoceras planula. This index is used for the upper part of
the zone, above the range of E. bimammatum, following Salfeld (1913),
Wegele (1929), and Dieterich (1940). At the top is a band ('zone') of
Taramelliceras wenzeli (Oppel) (refigured Dieterich, 1940). According to
Dieterich, Ringsteadiae do not range above the middle of this subzone,
in which case there is presumably a gap above the Pseudocordata Zone
in England and France; this again points to the Pseudocordata and Baylei
Zones being mere wisps of zones (their total thickness may be only a few
feet). 'Rasenia' dacquei and 'R.' perisphinctoides Wegele (1929, pi. x
figs. 1, 2) from this subzone, transferred to Pictonia by Schneid (1940),
are neither. The latter species can be matched almost exactly by what is
presumably a Ringsteadia in my collection from the Pseudocordata Zone
of Westbury, Wiltshire. The former may be a tumid and coarse-ribbed
offshoot of Pseudarisphinctes, or even a side-shoot from the stock of
Ringsteadia perisphinctoides (Wegele), but it is not strictly congeneric
with anything else yet published. There are numerous other interesting
Perisphinctids (figs, in Wegele, 1929), largely assignable to Decipia and
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