Arkell.1956.Jurassic..

572 MEXICO AND THE GULF REGION
representatives of both Tithonian and Neocomian, even though Upper
Tithonian ammonites have not been found. This might account for the
inclusion in the collections of so many anomalous uncoiled ammonoids
of strongly Cretaceous affinities.
The Middle Tithonian having received expert treatment in the readilyaccessible
monograph by Imlay (1942) there is no need to list the
species. The genera include Phylloceras, Metahaploceras, Pseudolissoceras,
Hildoglochiceras, Simoceras, Virgatosimoceras, Aspidoceras, Physodoceras,
Virgatosphinctes, Corongoceras, Dickersonia, Micracanthocer as, Durangites,
Lytohoplites, Parodontoceras, Berriasella, Spiticeras and various 'heteromorphs'.
Dickersonia has not been found outside Cuba. Three species of
'Berriasella! are added by Sanchez Roig (1951, pis. 21, 22), but one (pi. 22,
figs. 3, 4) seems to be an Oxfordian Dichotomosphinctes (? aff. ouatius Buck.).
It can perhaps be assumed that a similar mistake in collecting was responsible
for the record by Brown & O'Connell (1922) of Bajocian in Cuba
on the strength of a Strenoceras sp. nov., considering the strong resemblance
to this genus of some Cuban Corongoceras and Dickersonia (cf.
Imlay's pis. 5 and 6). No ammonites earlier than Upper Oxfordian
have ever been figured from Cuba, although Bajocian and Bathonian
have been quoted without evidence (Schuchert, 1935, p. 520; Palmer,
1945, p. 6).
The rich Upper Oxfordian fauna, on the other hand, still lacks a reviser.
Figures of variable quality (some unrecognizable) have been published
by Sanchez Roig (1920, 1951), O'Connell (1920) and Jaworski (1940).
Dr Sanchez Roig in his latest paper (1951) still assigns some of the forms
to Kimeridgian genera {Ataxioceras and even Virgatosphinctes) but these
are misidentifications. In my opinion his Virgatosphinctes (pi. 20, figs.
1, 2) is the inner whorls of an Upper Oxfordian Perisphinctes sensu
stricto, and his Ataxioceras lictor cubanensis (pi. 23) is a typical Arisphinctes,
close to P. (A.) ringsteadensis Arkell, and its date is early-Bimammatum
Zone; it has no resemblance to Progeronia lictor (Fontannes) of the
Kimeridgian. Jaworski (1940, p. 134) and Imlay (1952, p. 969) were right
in concluding that all the ammonites from the Jagua formation figured
hitherto either are Upper Oxfordian or belong to peculiar local subgenera
or genera (such as Vinalesphinctes), some not yet named, but not inconsistent
with a Bimammatum Zone dating. Having been concerned with
European Perisphinctids of Oxfordian age for more than thirty years, I
think it worth while to attempt a revision on the basis of the published
figures. Professor Jaworksi sent me a few specimens from Cuba before
the war and my comments are incorporated in his valuable paper (1940,
pp. 124, etc.). The extraordinary suture of Perisphinctes plicatiloides
as figured by O'Connell, which I pointed out (1939, Mon. Am. Engl.
Corallian Beds, p. 149) seemed to set it apart from all European subgenera,
was found by Jaworski (1940, p. 120) to have been misinterpreted.
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