Conus sextoni (Hoerle, 1976)
Diagnosis (1):
Shell low spired; slender;
periphery about one-fourth distance in front of shoulder; tapering anteriorly
with a suggestion of a slight twist to the left. Adult specimen consisting of
two and one-half rounded nuclear whorls and seven teleoconch whorls. Sutures
distinct, slightly impressed. Summits of early post-nuclear whorls flat, those
of later whorls convex with an adaxial slope, forming a slight concavity in
front of suture.
Whorls ornamented by prominent,
but not crowded, moderately arched growth lines. Anal notch shallow; outer lip
nearly straight. Sculpture of last whorl consisting of broad , flat bands
separated by narrow, increm entally striated grooves; growth lines prominent, giving
the shell an axially roughened appearance.
Dimensions of holotype: height
19.0 mm (incomplete), diameter 9.2 mm.
Holotype: USNM 647645.
Type locality: TU 951, Ten Mile
Creek, about 1 ¼ miles
west of Chipola River (SE ¼ Sec.
12, T1N, R10W), Calhoun County, Florida.
Occurrence: Chipola Formation, Florida; late lower Miocene.
Figured specimen: USNM 647645. (holotype).
Discussion: C. sextoni is represented only by the type specimen
and does not appear to be allied to any other Conus species from the Chipola
Formation. It cannot definitely be stated at this time if the bands and narrow
grooves, completely covering the final whorl, are a constant feature of this
species as, generally, the extent of ornamentation of the last whorl is a
variable factor, e.g., C. chipolanus Dall. The two and onehalf whorl
nucleus, the lack of ornamentation of the early whorls and the uniquely formed
summits of the spire whorls easily differentiate this species from ot her Conus of the Alum Bluff Group. The only other
fossil cone to which this new species bears a resemblance, and only
superficially, is C. cruzianus Dall, 1890, from the Pliocene limestone of the " Island of Santa
Cruz, West Indies" [St. Croix, U.S. Virgin Islands]. The one feature C. sextoni and C. cruzianus have in common is a slight channel
in front of the suture. The ornamentation on the last whorl of C. cruzianus consists of rounded, finely
striated cords, the posterior ones medially sulcated , as contrasted to the
bands and grooves of C. sextoni.
A Recent Caribbean species, C. granulatus Linne , 1758, has the final whorl
sculpture similar to C. sextoni but the spire characteristics are entirely different. Treatment failed
to reveal any color pattern and so it must be assumed that in life the shell
was unpatterned, unlike C. granulatus, which has strong shoulder mar kings.
This shell is named in honor of
Mr. Cecil Sexton, Altha, Florida, who has generously permitted workers to
collect at TU 951, which is located on his property.
Conus cruzianus (Dall, 1890)
Shell elongate pyriform, thin,
deeply spirally sulcated; whorls ten or twelve, apex
acute, arising from a spire but little elevated, and having its slope concave in profile; sides of the shell
with about twenty deep, uniform rounded sulcations,
separated by slightly narrower cords ; anteriorly these cords are rounded and finely striated spirally,
midway they are a little flattened, and
near the spine they are even marked with a shallow median sulcus; the channels
are not striate between the cords, or but in the faintest manner; sides of the shell slightly swelling, falling
away toward the spire, which is rounded at the
margin, striated with fine distinct threads, and with a narrow striated channel
close to and in front of the suture; transversely the sculpture is only of lines of growth, which cover the whole
shell, but are not prominent ; aperture narrow, especially behind, posterior
angle hardly notched, pillar straight, simple.
Max. lon. of shell 27.5 ; of aperture 23.0 ; max. lat. of shell 13.3 mm.
White Tertiary (Pliocene ?) limestones of the
Island of Santa Cruz, West Indies.
This shell, now pure white, retains traces of
yellow flammules on the spire, radiating
from the apex, and irregular yellowish blotches on the sides.
This species is of entirely different form from C.
planiliratus Sowerby, C. gracilissimus
Guppy, C. aratus Gabb and other Antillean sulcate cones.
C. bonacsyi Gabb has also a widely different form, with the spire unstriated. I judge of Gabb's species, of
course, by his types at Philadelphia, as the fossils have never been figured. I have had
this species for a long time, and take this
opportunity of figuring it.
St. Croix
is the only one of the islands between Vieques and the Anegada Passage that is
known to have any Miocene beds, which again consist of limestone carrying
Orthaulax aguadillensis Maury. It seems quite safe to correlate this
Orthaulax-bearing limestone with the Quebradillas limestone, which is
widespread and transgressive in Porto Rico and along the south edge of the
Virgin Bank. St. Croix is the type locality of Conus cruzianus Dali, which
seems to have been ignored. It probably was collected from the lower Miocene
limestone.
|
|
|
Conus sextoni (1)
Holotype, USNM 647645 mm. 19,0 x 9,2 Chipola Formation, Florida Miocene |
Conus cruzianus (2)
mm.
27,5 x 13,3 Pliocene
? Island of Santa Cruz, West Indies |
Bibliografia
Consultata
·
(1) - Hoerle, S. E.,
1976. The
Genus Conus (Mollusca: Gastropoda) from the Alum Bluff Group of
Northwestern Florida. Tulane Studies in Geology and Paleontology, 12 (1 )
·
(2) -
Dall, W. H., 1890. Tertiary Mollusks of Florida. Transactions of the
Wagner Free Institute of Science of Philadelphia, 3