PLIENSBACHIAN (LOWER JURASSIC) BIOSTRATIGRAPHY AND ...

specimens are also similar to Imlay’s (1968, 1981)
figured specimens of A . sp. cf. A . algovianum from
Alaska and the western United States, except that
Imlay’s material tends to have a wider whorl section
and slightly coarser ribbing.
Wiedenmayer (1980) tentatively placed Imlay’s
(1968) A . sp. cf. A . algovianum in the genus
Oregonites Wiedenmayer (1980), which is characterized
by forms with a depressed whorl section and coarse
ribs of irregular relief that are often paired at the base
of the flanks. Imlay’s (1968) material is here retained
in the genus Arieticeras. The question as to whether or
not the genus Oregonites is valid, or if the specimens
assigned to it (Wiedenmayer, 1980) are variants of the
European genera A rieticera s, C anavaria, F o n t-
anelliceras, or Fuciniceras, was raised by Braga (1983).
The Spatsizi specimens differ from the lectotypes of
A . algovianum [Schroder, 1927, designated by
Wiedenmayer (1977)] by their coarser, more sinuous
ribs.
Occurrence. Arieticeras algovianum is common in the
Upper Pliensbachian of Tethys. It is reported from
Morocco, Spain, southern France, Italy, Switzerland,
and as far north as southern Germany. In North
America it occurs in the western United States, British
Columbia, and southern Yukon where it is found
associated with Leptaleoceras and Fanninoceras.
The Spatsizi material was found at localities 17-19,
31, 42, 49, 57, 58, 62, 63, 66, and 74.
Age. Late Pliensbachian (Kunae Zone).
Arieticeras sp. cf. A . ruthenense (Reynes, 1868)
Plate 15, figures 1, 2
cf. *1868 A m m o n ites ruthenense Reynes, p. 94,
PI. 2, fig. 4a-c.
non 1909 Seguenziceras ruthenense (Reynes) emend.
Meneghini. Rosenberg, p. 291, PI. 15,
fig. 2a-c.
cf. 1934 A rie tic e ra s ru th e n e n se (Reynes) var.
typique Monestier, p. 59, PI. 8, figs. 2, 4,
5, non figs. 1, 12, 19.
cf. 1934 A rie tic e ra s ru th e n e n se (Reynes) var.
m eneghiniana Monestier, p. 59, PI. 8,
figs. 39, 40, non fig. 38; non PI. 11, fig. 2.
non 1964a A rieticeras aff. A . ruthenense (Reynes).
F re b o ld , p. 14, PI. 4, figs. 3, 4
(= Leptaleoceras sp.)
71968 Fuciniceras cf. F. acutidorsatum Kovacs.
Imlay, p. 41, PI. 7, figs. 22 and 24 only,
cf. 1977 A r i e t i c e r a s r u t h e n e n s e (R e y n e s ).
Wiedenmayer, p. 85, PI. 16, fig. 17; PI. 17,
fig. 3 (and synonymy),
cf. 1980 A r i e t i c e r a s r u t h e n e n s e (R e y n e s ).
Wiedenmayer, p. 115, PI. 20, figs. 21-24;
PI. 21, figs. 1, 2.
Material. Nine specimens, poorly to moderately well
preserved as external and internal moulds in calcareous
concretions.
M easurements.
Specimen D UD U W H W H D PR H W
GSC 83120 47 17 36 15 32 21
GSC 83121 50 2! 42 19 38 23
D escription. Shell evolute, whorl section elliptical.
Umbilical wall low; umbilical shoulder rounds onto
convex flanks. Ventrolateral shoulder rounded, venter
convex, distinctly carinate; keel bordered by shallow
sulci.
Ornament consists of simple, straight to slightly
sinuous ribs that arise on the umbilical shoulder, trend
rectiradiately to slightly rursiradiately on the flanks,
and project slightly at the ventrolateral shoulder. Rib
strength may vary with growth on a single specimen or
between specimens; both fine to moderately coarse ribs
are observed on the Spatsizi material.
Discussion. According to Braga (1983), the status of
the species A . ruthenense, and its relationship to other
species in the genera Arieticeras and Leptaleoceras is in
question, a problem reflected in the complexity and
length of the synonymy for A . ru th e n e n se in
Wiedenmayer (1977). Braga (1983) pointed out the
morphological similarity between L eptaleoceras
accuratum and A . ruthenense and concluded that
perhaps the two forms are best considered as end
members of a continuous morphological series. In this
study, A . ruthenense is retained, as specimens from the
Spatsizi collection assigned to A . sp. cf. A . ruthenense
possess generally coarser, straighter, and less densely
spaced ribs, and a less compressed whorl section than
specimens here assigned to L . sp. aff. L. accuratum.
Arieticeras sp. aff. A . algovianum has coarser, more
sinuous ribs than A . sp. cf. A . ruthenense.
Occurrence. Arieticeras ruthenense has been found in
the Tethyan region of Europe and North Africa
(Wiedenmayer, 1977, p. 85). Its distribution in western