Conus (Lithoconus) tortilis (Conrad, 1855)

Descrizione e caratteristiche:

Conus ovato-turbinato; spira conico-obtusa con apice acuto; gli avvolgimenti sono appiattiti in senso obliquo e presentano linee spirali e rigature trasversali, l’ultimo giro è carenato vicino alla base e diritto tra la carena e la sutura; le linee di accrescimento sono ampiamente curvate; la base presenta rigature profonde e fitte. Si differenzia dal Conus sauridens per le spire più prominenti e convesse e per il callo alla base ampio e contorto⁽¹⁾. Per Meyer il Conus tortilis ed il Conus alveatus sono varietà del Conus sauridens⁽²⁾.

Il Conus tortilis viveva in acque poco profonde come il Conus alveatus ed il Conus sauridens⁽³⁾.

Conus (Leptoconus) tortilus Conrad (Plate 26, figures 1, 4, 6, 8, 13)

1854. Conus tortilus CONRAD, in WAILES, Rept. agriculture and geology Mississippi, p. 289 (name only), pl. 15, fig. 5.

1855. Conus tortilis CONRAD, Acad. Nat. Sci. Philadelphia, Proc., 1st ser., vol. 7, pp. 257, 260.

1937. Conus (Lithoconus) sauridens Conrad (part). PALMER, Bull. Am. Paleontology, vol. 7, no. 32, pp. 458-459.

"Ovato-turbinate; spire obtusely conical with the apex exserted, acute; whorls obliquely flattened, with revolving impressed lines and transverse wrinkles, carinated near the base, direct between the carina and suture; lines of growth on body whorl profoundly curved; base with a profound thick fold." Conrad, 1855.

TYPE LOCALITY: "Green-sand marl bed of Jackson, Miss."

HOLOTYPE: Acad. Nat. Sci. Philadelphia 13196.

A very fine specimen in our collections from Montgomery, Louisiana, is 90 millimeters high and 50 millimeters in diameter. The height of the spire is only about one ninth the total height of the shell. There are at least 15 whorls, the first 2 or 3 included in the small but high smooth polished proto-conch. The next few whorls are crenulated at the shoulder, and the succeeding whorls are rimmed with a smooth and somewhat polished and slightly raised margin. Between the rim and the suture, the shoulder is closely lirate, and the lirae are reticulated by feebly arcuate incrementals. The periphery of the body of the adult is subacute, the sides evenly converging to the truncate anterior extremity. The aperture is narrow, only the width of the shoulder, and the sides subparallel. The shoulder notch is very shallow, the flare of the outer lip pronounced. There is a pad of callus on the inner wall at the anterior fasciole, and behind it a slight depression. The fasciole shows a scarcely perceptible bulge and is feebly lirate.

Although the adults of Conus tortilus are readily separable from C. santander and C. sauridens of the Claiborne, the earlier rating of C. tortilus as a subspecies of sauridens of authors is understandable. The restricted C. sauridens from the eastern and C. haighti from the western Gulf of Mexico have higher spires than C. tortilus, but the Jackson species seems little more than a greater C. santander with a slightly lower spire and increased girth. The characters of the earlier whorls, the few sculpture details, the flare of the outer lip, and the flattened and callused anterior extremity of the columella are similar in both.

FIGURED SPECIMENS: U. S. Nat. Mus. 497097 and 497098 from U.S.G.S. is. 13598 (L-11), at Presa El Mescal, Zacate, General Bravo, Nuevo León; U.S. Nat. Mus. 497099 from U.S.G.S. is. 13504 (M-8), 15.9 kilometers S. 7° 30′ E. of Ciudad Camargo, Tamaulipas; and U.S. Nat. Mus. 494949 from U.S.G.S. is. 13506 (M-7), 13.5 kilometers S. 12° E. of Ciudad Camargo, Tamaulipas, Mexico.

DISTRIBUTION: Jackson formation: lower or middle Jackson, U.S.G.S. sta. 13506 (M-7); U.S.G.S.. sta. 13504 (M-8). Upper Jackson, U.S.G.S. sta. 13598 (L-11); U.S.G.S. sta. 14009 (M-13).

MBC-2: Moodys Branch fm., MS, 38 Ma ⁽³⁾

L’incorporazione dello stronzio nel guscio aragonitico dei gasteropodi è influenzato principalmente dalla temperatura, non dalla velocità di crescita⁽³⁾.

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Bibliografia Consultata

• (1)  - T. A. Conrad (1855) “Observation on the Eocene deposit of Jackson, Mississippi, with description of thirty-four new species of shells and corals”, Proceeding of The Academy of Natural Sciences of Philadelphia, Philadelphia

• (2)  - Meyer (1885) “Species in the Southern Old-Tertiary”, The American Journal of Science – Third series – Vol. XXIX

• (3)  - Sindia Maria Sosdian (2008) “CLIMATE TRANSITIONS ACROSS THE CENOZOIC: INSIGHT FROM ELEMENTAL RATIOS IN BENTHIC FORAMINIFERA AND MARINE GASTROPODS”, A Dissertation submitted to the Graduate School-New Brunswick Rutgers, The State University of New Jersey