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

416 GEOLOGY AND PALEONTOLOGY OF CANAL ZONE
The minute shells from the middle part of the Gatun
formation include five specimens, all consisting only of
the protoconch and the first post-protoconch whorl, of
a noteworthy Acteon noteworthy for its exception­
ally large protoconch and nonplicate columella. The
large protoconch and strong, abruptly appearing sculp­
ture indicate that it is not closely allied to A. exilis,
the type of Lissacteon. In fact, it has no known close
allies.
The validity of Lissacteon as a subgenus is question­
able. The type species has a suggestion of a weak colu-
mellar fold, but there is no discontinuity in the
strength of the fold shown by species of the genus.
Occurrence: Middle part of Gatun formation (mid­
dle Miocene), eastern area, locality 14/Tb; western area,
localities 161c, I70a.
Genus Rictaxis Ball
Dall, Am. Jour. Conchology, v. 7, p. 136, 1871.
Type (orthotype): Rictaxis punctoccelata (Carpenter), (Tornatella
punctoccelata Carpenter), living, eastern Pacific
Ocean.
Rictaxis oryza (Gabb)
Actceonidea oryza Gabb, Acad. Nat. Sci. Phila. Proc., v. 24,
(1872), p. 273, pi. 11, figs. 8, 8a, 1873 (Miocene, Domini­
can Republic). Gabb, Am. Philos. Soc. Trans., v. 15, p.
245, 1873 (Miocene, Dominican Republic).
Rictaxis oryza (Gabb), Pilsbry, Acad. Nat. Sei. Phila. Proc.,
v. 73, p. 310, pi. 23, fig. 12, 1922 (Miocene, Dominican
Republic).
Small, slender. Visible part of protoconch consisting
of one whorl. End marked by appearance of sculpture.
Sculpture, of narrow, closely spaced, spiral grooves,
pitted by fine axial threads, covering entire whorl.
Aperture long, narrow. Columella bearing well up a
narrow fold, merging downward into long, narrow
columellar lip.
Estimated restored height 6 mm, diameter 2.7 mm.
Type: Acad. Nat. Sci. Phila. 3181.
Type locality: Dominican Republic, Miocene.
Though this rare species, heretofore represented only
by the type, is unequivocally identified, the seven spe­
cimens all from the lower and middle parts of the
Gatun formation are unsatisfactory for illustrating.
Four minute shells show the protoconch and first or
first and second, post-protoconch whorl. A mature body
whorl (locality 139c), which has more closely spaced
spiral grooves than the type, shows the apertural fea­
tures.
Rictaxis oryza is the monotype of Actceonidea Gabb,
proposed when the species was described. It is sole
named Caribbean species of a genus that survived until
Pliocene time in Florida, where it is represented by
R. myakkanus (Dall) (Olsson and Harbison, 1953, p.
158, pi. 25, figs. 5, 5a), and is now living in the eastern
Pacific Ocean. An immature shell from the late Mio­
cene Melajo clay member of the Springvale formation
of Trinidad (height 3.3 mm), which has a large pro­
toconch, may represent a second Caribbean species.
Occurrence: Lower and middle parts of Gatun for­
mation (middle Miocene). Lower part, localities 138c,
138e. Middle part, eastern area, localities 139b, 139c,
139g. Miocene (presumably Cercado or Gurabo forma­
tion), Dominican Republic.
Family RINGICTTLIDAE
Genus Ringicula Deshayes
Deshayes in Lamarck, Histoire naturelle des animaux sans
vertebres, 2d eel., vol. 8, p. 342, 1838.
Type (logotype, Gray, Zool. Soc. London Proc., p. 140, 1847):
Auricula ringens Lamarck, Eocene, western Europe.
Subgenus Ringiculella Sacco
Sacco, I Molluschi del terreni terziarii del Piemonte e della
Liguria, pt. 12, p. 16, 1892.
Type (logotype, Cossmann, Essais de paleoconchologie com-
paree, pt. 1, p. 115, 1895): Marginella auriculata Menard,
Miocene to present time, western Europe.
Ringicula (Ringiculella?) species
A crushed inflated Ringicula was found in the Cai-
mito formation on Pato Horqueto Island. The outer
lip is not preserved. Both columellar folds are narrow.
The parietal callus is thick, but the inner part of the
upper parietal wall, where the parietal fold of Ringi­
culella is seated, cannot be exposed without risk of
damaging the shell. All except the uppermost part of
the body whorl is sculptured with finely engraved,
spiral strise. The height is 3.3 mm, and the diameter,
minus the outer lip, but somewhat increased by crush­
ing, 2.5 mm.
Occurrence: Caimito formation, Gatun Lake area,
locality 55a.
Ringicula (Ringiculella) semistriata d'Orbigny
Plate 62, figure 12
Ringicula semi-striata d'Orbigny, in de la Sagra, Histoire phys­
ique, politique, et naturelle de Tile de Cuba, Mollusques,
v. 2, p. 103, pi. 21, figs. 17-19, 1841 (living, Jamaica).
Ringicula semistriata d'Orbigny, Gabb, Acad. Nat. ScL Phila.
Jour., 2d ser., v. 8, p. 358, 1881 (Pliocene, Costa Rica).
Pilsbry, Manual Conchology, v. 15, p. 399, pi. 46, figs. 43,
44, 1893 (1894) (living, Jamaica).
Ringicula tridentata Guppy, Sci. Assoc. Trinidad Proc., vol. 2,
no. 2, p. 76, 1873 (Miocene, Jamaica) ; reprint, Bull. Am.
Paleontology, v. 8, no. 35, p. 60, 1921.
Ringicula (Ringiculella) tridentata Guppy, Woodring, Carnegie
Inst. Washington Pub. 385, p. 132, pi. 2, fig. 22, 1928
(Miocene, Jamaica).