Geology and Paleontology of Canal Zone and Adjoining ... - USGS

426 GEOLOGY AND PALEONTOLOGY OF CANAL ZONE
The type is the only Gatun specimen of this inflated,
distinctive species: distinctive on account of its strong,
widely spaced, spiral strise. The "appearance of very
shallow longitudinal plication" on the swollen part of
the shell, recorded by Brown and Pilsbry, presumably
is the result of slight difference in shell composition.
If the type is mature, it is a minute species.
A minute translucent shell, from the Limon for­
mation in Puerto Limon, Costa Rica (USGS 21036),
is identified as Volvulella micratracta. It is a little
more slender than the type, and has five basal spiral
strise and six apical and a more acute apical spine. The
main part of the shell bears microscopic spiral linea-
tion.
Brown and Pilsbry compared their species with V.
minuta Bush (1885, p. 469, pi. 45, fig. 11), a similar
small, inflated western Atlantic species that lacks
strong, widely spaced, spiral strise, I am unable to
confirm the apical, axial sculpture shown in Harry's
(1967, p. 138, fig. 11) drawing of a specimen of V.
minuta identified by Bush (USNM 44773), and such
sculpture is not apparent 011 other specimens of her
species. Therefore Harry's synonymizing of V. minuta
with the larger, apically sculptured western Atlantic
species (Bulla acuta d'Orbigny, a junior homonym),
for which he adopted the name V. recta (Morch), is
rejected. V. recta, however, is a name of debatable
availability, as it is based on a lapsus calami.
Occurrence: Middle part of Gatun formation
(middle Miocene), Gatun Locks excavation (Brown
and Pilsbry's record). Limon formation (late Mio­
cene), Costa Rica.
Volvulella (Volvulella) cylindrica parallela
(Pilsbry and Johnson)
Plate 62, figure 17
Volvula parallela Pilsbry and Johnson, Acad. Nat. Sci. Phila.
Proc., v. 69, p. 151, 1917 (Miocene, Dominican Republic).
Pilsbry, Idem, v. 73, p. 313, fig. 11, 1922 (Miocene, Do­
minican Republic).
Moderately large, cylindrical, very slender, height
three times diameter. Apical spine short. Shell bearing
microscopic spiral lineation, and at both ends faint
spiral strise, those on apical part more distinct and
more widely spaced than those on basal part.
Height 4.7 mm, diameter 1.6 mm (figured specimen).
Type: Acad. Nat. Sci. Phila. 3188.
Type locality: Dominican Republic, presumably
Cercado or Gurbao formation.
A polished, cylindrical shell from the middle part
of the Gatun formation (presumably from the Gatun
Locks excavation) is referred to Volvulella cylindrica
parallela, which was based on three specimens in
Gabb's Dominican Republic collection. It is doubtful
whether these Miocene fossils can be distinguished
from the nominate subspecies of Carpenter's eastern
Pacific species (Harry, 1967, p. 141, figs. 6-9). They
closely resemble shells from the Panamic part of the
range of the nominate subspecies. No similar species
is living in the Caribbean region.
V. cylindrica parallela occurs also in strata of
middle Miocene age in southeastern Costa Rica
(USGS 5882g and other collections from Rio Banana).
Occurrence: Middle part of Gatun formation
(middle Miocene), eastern area, locality 159d. Miocene,
presumably Cercado or Gurabo formation, Dominican
Republic. Middle Miocene deposits, Costa Rica.
Volvulella (Volvulella) phoinicoides (Gardner)
Plate 62, figure 15
Volvula phoinicoides Gardner, U.S. Geol. Survey Prof. Paper
142, p. 268, pi. 37, fig. 26, 1937 (1938) (Miocene, Florida).
Of medium size, cylindrical, very slender, height
three times diameter. Apical spine very short or absent.
Entire shell bearing microscopic spiral lineation, gen­
erally somewhat coarser on basal part. Apical end of
aperture wide, outer lip extending to apex with gentle
slope.
Height 3.3 mm, diameter 1.1 mm (figured specimen).
Type: USNM 351037.
Type locality: USGS 3742, Shell Bluff, Shoal River,
Walton County, Florida, Shoal River formation.
Volvulella phoinicoides has the outline of V. cylin­
drica parallela^ but differs in apical features and sculp­
ture. Immature shells and mature shells that are
broken back show that a short spine is present at an
early stage regardless of its presence or absence at
maturity. The apical features are more or less inter­
mediate between those of Volvulella s.s. and those of
the subgenus Paravolvulella (Harry, 1967, p. 141; type
(orthotype) : Volvulella (Paravolvulella) texasiana
Harry, living, western Gulf of Mexico). The apical end
of the outer lip of Paravolvulella extends horizontally
to the apex of the shell and is slightly concave.
None of the 21 shells from the Gatun formation is as
large as the largest Florida shells, which reach a height
of 4.5 mm. This species evidently left no descendents.
Occurrence: Lower, middle, and upper parts of
Gatun formation (middle Miocene). Lower part, local­
ity 138c. Middle part, eastern area, localities 139b,
139c, 147b, 147g. Upper part, eastern area, locality
I77b. Shoal River formation (middle Miocene),
Florida.
Family SPIRATELLIDAE
Genus Spiratella Blainville
Blainville, Dictionnaire des sciences naturelles, v. 9, p. 407,
1817.