Vol. 98(3)
July 27, 1984
THE NAUTILUS 121
AGATHODONTA NORTONI. NEW SPECIES: LIVING MEMBER OF A
LOWER CRETACEOUS TROCHID GENUS
James H. McLean
Los Angeles County Museum of Natural History
900 Exposition Boulevard
Los Angeles, CA 90007
ABSTRACT
Agathodonta nortoni, new species, from archibenthal (300 meter) depths in the
Philippines, repr-esents a living record of a genus presum.ed extinct since the
Lower Cretaceous. It is assigned to the tribe Chilodontini, subfamily Margariti-
nae, in agreement with an earlier placem,ent of other living genera in this group.
In a preliminary report on classification of the
trochid subfamily Margaritinae (McLean, 1982),
I assigned such Recent genera as Euchelus
Philippi, 1847, Danilia Brusina, 1865, and Tur-
cica A. Adams, 1854, to the tribe Chilodontini of
the subfamily Margaritinae, a group previously
regarded as limited to the Mesozoic, Middle
Triassic through Upper Cretaceous. My alloca-
tion of these genera was based on a similarity of
sculpture, aperture shape, and apertural denti-
tion among the fossil and living genera.
Here I describe a new Recent species of the
chilodontine genus Agathodonta Cossmann,
1918, which until now had been known only in
the European Neocomian and Albian Stages of
the Lower Cretaceous, 110 to 135 million years
in age. This living link to such Mesozoic genera
as Pseudoclanculus Cossmann, 1918, Chilodon-
toidea Huddleston, 1896, Wilsoniconcha Wenz,
1939, Chilodonta Etallon, 1862, and the Recent
genera mentioned above is a further indication
that the Recent genera are related to the fossil
genera of the Chilodontini.
Shell characters of the chilodontine genera
are: clathrate sculpture, some expression of
apertural dentition, and an oblique aperture
with the entire apertural rim in the same plane,
enabling a close fit against the substrate. Living
genera have epipodial and radular features in
common, essentially as described by Beu and
Climo (1974) for their new species Danilia in-
sperata. Based on shell and radular characters,
Mirachelus Woodring, 1928, is also a member of
the group.
This and my earlier note (McLean, 1982), are
preliminary to a full revision of higher classifica-
tion in the Trochacea (in collaboration with C. S.
Hickman), in which epipodial and radular char-
acters of chilodontine genera will be illustrated.
Genus Agathodonta Cossmann, 1918
Agathodonta Cossmann, 1918: 200; Wenz, 1938: 296 [as
"Agnathodonta"]; Cox, in Knight et ai, 1960: 249. Type
species (original designation): Trochus dentigerus
Orbigny, 1843. Lower Cretaceous (Neocomian).
Agathodonta dentigera (Orbigny, 1843)
Trochus dentigerus Orbigny, 1843: 185, pi. 77, figs. 9-12.
Agathodonta dentigera, Cossmann, 1918: 200, pi. 7, figs.
8-11; Wenz, 1938: 298, fig. 653; Cox, in Knight et. al.
1960: 249, fig. 160, 2.
"High turbiniform, anomphalous, with strong-
ly convex whorls and base; ornament granose
spiral cords; columellar lip with two strong, ob-
tuse teeth." Cox, in Knight et al. (1960).
In addition to the type species, Cossmann
(1918) referred two other species to Agatho-
donta: Trochus guyotianus and T. tollotianus.
both of Pictet et Roux, 1849, from the Albian
Stage of the Lower Cretaceous.
Agathodonta is characterized by two pro-
nounced columellar plications, a trait shared
with the Jurassic Wilsoniconcha Wenz, 1939,
which differs in having a pupiform shape, and
the Recent Turcica, which has a much larger
shell with flat-sided whorls. Turcica was as-
signed by Keen, in Knight et al. (1960), to the
Monodontinae, but is related to Euchelus and
Danilia on the basis of radular, and epipodial
characters.
The genus Danilia, recently reviewed by Beu
& Climo (1974), differs irom Agathodonta in hav-
ing an exterior thickening of the final lip, and in
BioStor
