Conus chiraensis

Conus chiraensis (Olsson, 1930)

Descrizione e caratteristiche:

Shell small or medium-size; in porportions the height approximately twice the diameter ; the spire is flat to slightly elevated or
conic; shells with a flat spire, have a higher, projecting tip, formed of the nuclear and early post-nuclear whorls; in the higher spired forms, the outline of the spire is low, conic with a higher, projecting nuclear tip; sides of last whorl straight; shoulder of the body-whorl is sharply angled, below which the upper face of the whorl is usually feebly rounded or beveled;post-nuclear whorls about 8, with concave spire faces, lying between the high, ridge-like, peripheral edge of the whorl and the inner sutures; this concave zone sculptured with about 4 low, broad spirals and finer transverse (radial) lines; surface of the whorl below the shoulder is smooth, po^shed except for growth lines and feeble, irregular spirals on the anterior canal, the growth lines are straight below, curving above to the right and deeply retracted at the shoulder; anterior canal with 12 or more feeble, irregular spiral threads; aperture long, narrow.

Height 39mm. (broken) ; diameter 31mm.;

45mm. ; 28mm.;

32mm. (broken); 20mm.

Remarks.

The distinguishing characteristics of this Cone are the straight smooth sides, feebly sculptured with revolving spirals about the anterior canal; he spirally-sculptured spire whorls; and strongly retracted growth lines at the sharp shoulder angle. The flat spired shells illustrated by figure 2 is selected as the typical form. This is the dominant form in the older beds first appearing in the basal Talara of Yasila and Cunas de Jaquey near
Paita. The higher spired form illustrated by figure 1 is the common Oligocene variety, but all gradations occur between it and the flat-spired form.

This species resembles the Conus planiceps Heilprin from the Tampa Silex beds of Florida as figured by Dall 32 and the two species have probably a common ancestor. The Conus sauridens Conrad from the Jackson Eocene and C. alveatus Conrad from Vicksburg belong to the same group, but both species have the spire-whorls more concave.

Locality and Geologic Occurrence. — Talara formation, Yasila and Jaquey de Cunas. Saman formation, Lagunitas, Casa Saman. Chira formation, near Casa Saman, Quercotilla. Mancora formation, Que. Charanal.


Conus chiraensis Cotype mm. 40 Plate 5 – fig. 1 Oligocene	Conus chiraensis Cotype mm. 40 Plate 5 – fig. 10 Oligocene

Conus chiraensis Holotype 24212 mm. 46 Plate 5 – fig. 2 Oligocene	Conus chiraensis Cotype mm. 28 Plate 5 – fig. 4 Oligocene