Publicaciones Geolo_gicas Especiales Del lngeominas

ZONATION OF TilE CRETACEOUS OF CENTRAL COLOMBIA BY AMMONITES 19
and tend to fonn bundles some of which beco·
me more prominent near the adumbilical third
of the whorl side that appelll'll
as a surface covered
with irregularly distributed pleats. The section
of the whorl has a broadly rounded venter
and flattened diverging flanks which at the urn·
bllical rim attain their ,!Daximum width and
then tum abruptly into the. oblique umbical rim.
No living chamber is available.
DIAGNOSIS. This species is characterized
by: A) the callused ad umbilical half of the whorl,
B) the channel-like intercostal spaces, the broa·
dly arched trend of the fme rounded ribs on the
flanks, and their feeble projection on venter,
C) the whorl section with broadly rounded
venter and central third of the flank flattened,
and D) the plano concave adumbilical surface.
Meuurementl D Euw H W DfEuw % D/H.04
Holotype 46 6 24 18 13 54
COMMENTS. On Riedel's specimen of
Phylloceras velledae Mich. var. seresitensis Perv.,
from Utica, not far from the region studied in
the present report, (see especially Riedel's illus·
tration of the internal whorl, pl.4, fig.6) the
adumbilical half of the whorl is eroded so the
callused co,yering and urdrlying fme. ribbing
can not be recognized, but Riedel remBl'ks:
"Los flancos estan cubiertos de numerosas listas
finas que, naciendo aproximadamente a media
altura de las espiras, siguen derecho bacia el
!ado extemo, donde forman un arco apenas
perceptible hacia adelante". Riedel commented
that his specimen does not' show the falciform
trend o"f the ribs as in Ph. velledae Michelin (see
the figured cast of the neotype of this species in
Wiedmann, 1963, pl.12). The lectotype of Ph.
seresitense Pervinquiere (1910, p.9, Fig. 2, pl. 1,
Fig. 1; se·e Wiedmann, 1963, p.222) shows a
flattened surface of the flanks that descends
funnelwise to the umbilicus, this surface is
reduced to a mere rim around the umbilicus in
Riedel's figured specimen and in the present
specimen.
Wiedmann, the last reviewer of the
group (1963), recognized three "subspecies" of
Ph. seresitense based on the section of the whorl
and the width of the umbilicus. In the present
species the umbilicus is narrow and the section
of the whorl, like that figured by Riedel (1938
pl,. 12, Fig. 5) has a broadly rounded periventrai
shoulder rather than beveled shoulders as seen
i the lectotype of PerVinquiere (1910, pl. 1,
F1g. lb) and the hypotype figured by Wiedmann
(1963, pl.21, Fig. 1b).
. The. flattening of the flanks in the Colom-
bian spcunens produces a middle third of the
whorl 11de that diverges from the venter and
en pptly rounds into the umbilicus; in Per­
\'Ulqulere s illustrations, both middle and
adumbilical thirds of flanks are flattened but
sho"! . a. tendency to converge toward the
umb1cal rim. Wiedmann used the flattening of
the s1d s as a specific character (1963, p.202·
203, F1g_. 47b): Phy/locerrl$ (Hypophylloceros)
subserec1tense Wiedmann. The trend of the ribs
In the latter species is radial to slightly concave
adorally (?) (op.cit., pl. 15, Fig. 6) on flanks.
The subspecies P. (H.) seresitense tanit Pervin·
quilre (Wiedmann, p. 228, fig. 54) has a biconcave
type of ribbing.
This new species is named in honor of
Dr. Jost Wiedmann, of the Tiibingen Universitat,
West Germany.
OCCURRENCE. Capotes Member. Lower
Albian. Paja Fonnation (Arcillolitas abigarradas
Segment E.). Upper Aptian.
Family GUJ R;;cTIDAE
Genus \E