THE NAUTILUS 103(4): 143-148, 1990
Page 143
A New Fossil Land Snail (Gastropoda: Pulmonata: Polygyridae)
from the Middle Miocene of Northern Florida
Kurt AufTenberg
Roger W. Portell
Florida Museum of Natural History-
University of Florida
Gainesville, FL 32611, USA
ABSTRACT
A new fossil land snail, Praficalella prisca n sp., is described
from the C'harlton Member of the Coosavvhatchie Formation
(middle Miocene) at Brooks Sink, Bradford (>ounty, Florida.
This new species is assigned to Praticolella s.s. Martens, 1892
based on sculpture, palatal lip expansion and a narrow con-
striction behind the lip. This subgenus is presently confined to
central and southern Texas and Mexico under environmental
conditions known to have occurred in northern Florida during
the Miocene. Praticolella prisca n. sp. appears to be the earliest
know n member of the genus.
Key words: Gastropoda; Polygyridae; Praticolella. Miocene;
Florida.
INTRODUCTION
Collections of invertebrate fossils containing a new species
of terrestrial gastropod, Praticolella prisca n. sp., were
made by the authors in the mid 1980's from Brooks Sink,
a large, nearly circular, vertical-walled sink hole located
16.89 kilometers west of Starke, Bradford County, Flor-
ida (figure 1 ). Brooks Sink provides one of the best natural
exposures of Hawthorne Group sediments in Florida.
Exposed in approximately 23.0 meters of section are, in
ascending order, the Marks Head Formation, the undif-
ferentiated Coosawhatchie Formation, and the Charlton
Member of the Coosawhatchie Formation (figure 2).
The age of the Charlton Member (formerly Charlton
Formation) was considered to be Pliocene by Veatch and
Stephenson (1911) and Cooke (1943, 1945). Based upon
ostracods from this unit, identified by Harbans Puri as
middle Miocene and/or upper Miocene, Pirkle (1956)
reported the age to be older. More recently, Jones and
Portell (1988) recognized the middle Miocene clypeas-
teroid echinoid, Abertella aberti (Conrad, 1842) from
this unit. Huddleston (1988) assigned an age of middle
Miocene to the Charlton Member in Georgia based on
molluscan faunas, stratigraphic relationships, and the oc-
currence of several age-diagnostic planktonic foraminif-
era. Jones and Portell (1988) reported over 30 fossil in-
vertebrate taxa within the Charlton Member of the
Coosawhatchie Formation at Brooks Sink including Pra-
ticolella sp., the taxon described below.
MATERIALS AND METHODS
No fossilized shell material was recovered. The speci-
mens representing this taxon are preserved only as in-
ternal and external molds comprised of fine-grained do-
lostone. We use the term external mold to indicate the
impression in the matrix of the outer surface of the shell.
The matrix containing the external mold UF 14397 was
reduced and the specimen sonicated for observation of
the shell ultrastructure under a scanning electron mi-
croscope. Some of the specimens are incomplete in cer-
tain aspects. Nevertheless, standard shell parameters were
measured with vernier calipers whenever possible. All
specimens are reposited in the Florida Museum of Nat-
ural History, Invertebrate Paleontology Division, Uni-
versity of Florida, Gainesville, Florida 32611.
DESCRIPTION
Family Polygyridae Pilsbry, 1930
Subfamily Polygyrinae Pilsbry, 1895
Genus Praticolella Martens, 1892
Praticolella prisca new species
(figures 3-10, table 1)
Adult shell large (width 10.0-13.9 mm, height 6.7-10.0
mm); helicoid, depressed-globose, 0.64-0.72 times as high
as wide; spire moderately elevated, convex in outline
(figures 3, 6, 7); base round and inflated; the 4.6-5.0
convex whorls slowly increasing in size (figure 4); sutures
impressed; body whorl large, slightly flattened at suture,
round at periphery and below; deflection variable, slight-
ly upward or downward in the final 0.25 whorl, but
always descending very slightly before constricting and
inflecting; narrowly constricted posterior to palatal lip,
more deeply constricted along base (figures 4, 6); um-
bilicus narrow, tubular, about 0.10 the diameter of shell
and partially covered by reflected columellar lip (figures
5, 8); the 1.7 protoconch whorls are smooth except for a
BioStor
