|
|
|
|
|
|
|
|
|
|
Conus (Leptoconus) hornii (Gabb, 1864)
Conus hornii umpquaensis (Hendon in Turner, 1938)
Conus horni piruensis (Squires L.R., 1987)
Descrizione
e caratteristiche:
E’ una conchiglia biconica in modo molto diseguale; la parte relativa alle spire è molto bassa; presenta 7 ½ - otto giri, concavi nella parte superiore con un angolo acuto, con una scanalatura simile ad un filo proprio all’interno del margine. Il labbro è lungo, stretto e rettilineo, curvato e prominente nella parte superiore. Il profilo dell’ultimo giro è rettilineo. Alla base sono presenti poche scanalature oblique; talvolta sono evidenti una o due scanalature anche nella parte superiore dell’ultimo giro.
Questa specie fu rinvenuta per la prima volta presso Alizos Creek, vicino al vecchio Fort Tejon, dal Dr. Horn, da cui la specie prende il nome. Successivamente furono trovati numerosi esemplari presso la località 244 (Live Oak Canyon). Le principali caratteristiche che contraddistinguono questa specie sono la completa assenza di noduli o granulazioni sulla circonferenza esterna delle spire e la spalla leggermente concava (2).
L’esemplare illustrato proviene dal Venezuela: esattamente come per l’immagine sotto riportata (1) si può individuare una parte della spalla liscia e perfettamente diritta seguita dalla zona nella quale la spalla si presenta concava.
Distribuzione:
Eocene.
Dalla California fino al Venezuela (provincia del Gatun(3)).
|
|
|
|
|
|
|
|
|
|
Conus horni piruensis (Squires L.R., 1987)
Diagnosis (5).
Generic assignment based on inverted conical shape and high aperture with parallel sides. Specific assign-ment based on moderately high spire, angulate body whorl, and spire whorls concave with a few spiral ribs. Subspecific assignment based on numerous spiral ribs in concave portion of body whorl posterior to unnoded angulate shoulder.
Conus hornii piruensis new subspecies is most similar to Conus hornii umpquaensis Turner (1938:69, pl. 15, figs. 1, 2; Vokes, 1939:127, pl. 18, fig. 2; Weaver, 1943:510-511, pl. 96, fig. 18; Stewart, 1946:pl. 11, fig. 6; Givens and Ken-nedy, 1979:87, tables 1, 3; Squires, 1984:39, fig. 9n) from middle Eocene strata ("Domengine" through "Transition" "Stages"), San Diego, California through southwestern Ore-gon. Conus hornii piruensis differs from C. hornii umpquaensis in having spiral ribs over the entire shell surface rather than only on the anterior portion of the body whorl.
Conus hornii piruensis new subspecies is similar to Conus submonilifer Anderson and Hanna (1925:99-100, pl. 8, fig. 6) from upper Eocene ("Tejon Stage") strata, Kern County, southern California. Conus hornii piruensis differs from C. submonilifer in the following features: spiral ribs over the entire shell surface rather than only on the body whorl, concave-sided spire whorls rather than almost straight-sided, and no traces of nodes on the shoulder of the whorls.
Conus hornii piruensis new subspecies is somewhat similar to Conus hornii Gabb (1864:122, pl. 29, fig. 226; Dickerson, 1915:pl. 11, figs. 9a-c; Anderson and Hanna, 1925:99; Stewart, 1927:415, pl. 29, fig. 16; Givens, 1974:92, pl. 10, fig. 12) from upper Eocene ("Tejon Stage") strata, central Transverse Ranges, southern California. Conus hornii piruensis differs from C. hornii in the following features: slightly higher spire (one-third rather than one-fifth of shell height), spiral ribs over entire shell surface, numerous spiral ribs rather than only a few in concave portion of body whorl posterior to shoulder, and absence of fine groove just posterior to the body whorl shoulder.
Conus hornii piruensis new subspecies superficially resembles Conus weaveri Dickerson (1915:74-75, pl. 11, fig. 10; Anderson and Hanna, 1925:101-102; Weaver, 1943:512, pl. 96, fig. 26) from the upper Eocene Cowlitz Formation, south-western Washington. Conus hornii piruensis differs from C. weaveri in the following features: narrower shell, higher spire, seven rather than three or four fine spiral ribs posterior to penultimate whorl shoulder, nine rather than five fine spiral ribs posterior to body whorl shoulder, less concave in area between suture and whorl shoulder, absence of nodes on spire whorls or on adapical half of body whorl shoulder, and stronger spiral ribs on middle portion of body whorl. Contrary to Dickerson's (1915) description, the holotype of C. weaveri is noded, with nodes on the shoulder (i.e., small nodes starting on the adapical half of body whorl shoulder and increasing in size toward the spire apex).
Description. Shell small, biconical, seven to eight whorls, impressed sutures, moderately high spire, approximately one-third of shell height. Protoconch missing. Spire whorls concave, lowermost portion of whorls angulate and slightly bead-ed in upper spire whorls. Upper spire whorls with about three fine spiral ribs, penultimate whorl with four fine spiral ribs on posterior half and three very fine spiral lirae on anterior half. Body whorl concave posterior to angulate shoulder, with five fine spiral ribs on posterior half of concavity and four very fine spiral threads on anterior half. Body whorl flat-sided anterior to shoulder and covered by numerous well-incised spiral ribs that become stronger and more closely spaced anteriorly.
Aperture long and narrow. Inner lip obscured by matrix. Holotype height (complete) 14 mm, width (complete) 8 mm.
Primary Type Material. LACMIP holotype 7500, Matilija Sandstone?, CSUN locality 237.
Molluscan Stage Range. "Domengine."
Geographic Distribution. Whitaker Peak area, southern California.
|
|
|
|
|
|
|
|
Bibliografia
Consultata
