Conus ligatus

Leptoconus ligatus (Tate, 1890)

Descrizione e caratteristiche:

Shell biconic; spire of variable height, but usually moderately low, consisting of about seven gradated whorls, ending in a small naticiform pullus of one and a-half smooth whorls; body-whorl more or less subpyriform. Spire-whorls with an obtuse thick shoulder, the two slopes inclined approximately at a right angle and of about equal width; the posterior area is usually flat or slightly concave, rarely with a slight upward inclination; it is ornamented with four or five spiral threads, separated by narrower furrows, and rather close-set striae of growth, conformable with the anal insinuation of the outer lip; the anterior area is provided with one or two threadlets margining the rib-like keel.

Body-whorl varying from pyriform to elongate-ovate, the peripheral keel defined anteriorly by a linear constriction, posterior to which there are one or two threads on the peripheral band. The surface is sculptured at the posterior part with incised linear lines, which towards the front become wider, and are finally replaced by ribs narrower than the shallow interspaces; the whole is crossed by growth-lines, which produce punctations in the linear sulci, and a fenestrated ornament anteriorly. The strength of the encircling lines is variable, and may be obsolete in the posterior half of the body-whorl. The aperture is narrow, with a short anal sinus corresponding with the posterior slope of the whorl; the outer lip is conspicuously ecurved medially ⁽¹⁾.

Dimensions. — Of a large typical example. Length, 41 mm.; greatest width, 22; length of aperture, 34; length of last whorl, 35. Of a pyriform variety, the corresponding measures are 32, 20, 27.5, 28.5 .

Localities. — Eocene beds at Muddy Creek and Schnapper Point ⁽¹⁾.

Affinity. — This species exhibits much individual variation in shape of body-whorl and length of spire, but presents in the cord-like appearance of its peripheral keel a character which readily distinguishes it from other Australian species. A figured variety so closely resembles C. deperditus of the Hampshire and Paris basins, that it is only by comparison of actual specimens possible to separate them. Though in this individual the gradation of the spire and the peripheral rib have lost much of their prominence, yet the defining threads on the keel are present — a character absent in C. deperditus; moreover, the latter is further distinguished by having two spiral and distant threads on the posterior area of the whorls. At the same time, the Australian similitude is no more than an extreme variation from a type which is obviously distinct from C. deperditus ⁽¹⁾.

However, it may be well to note that our Australian Cones are very difficult of specific definition, so much so that it is possible to bring all the species into very close relationship, through extreme individual variability ⁽¹⁾.

E’ una conchiglia biconica, la cui spira ha altezza variabile, ma in genere moderatamente bassa, ed è costituita da circa sette spire graduate, terminanti in un piccolo pullus naticiforme di una spira e mezza, liscia; corpo-spirale più o meno subpiriforme⁽¹⁾.

La spira è a guglia, con spalla spessa ottusa, i due versanti inclinati approssimativamente ad angolo retto e di larghezza circa uguale; l'area posteriore è generalmente piatta o leggermente concava, raramente ha una leggera inclinazione verso l'alto; è ornato da quattro o cinque fili a spirale, separati da solchi più stretti, e striature piuttosto ravvicinate di crescita, conformabile con l'insinuazione anale del labbro esterno; l'area anteriore è provvista di uno o due filetti che delimitano la chiglia a coste⁽¹⁾.

Corpo-spirale variabile da piriforme ad allungato-ovato, la chiglia periferica è definita anteriormente da una costrizione lineare, posteriormente alla quale sono presenti uno o due fili sulla fascia periferica. La superficie è scolpita nella parte posteriore con linee lineari incise, che verso la parte anteriore si allargano, e sono infine sostituite da nervature più strette delle intercapedini poco profonde; il tutto è attraversato da linee di crescita, che producono punteggiature nei solchi lineari, e un ornamento fenestrato anteriormente. La forza delle linee che circondano è variabile e può essere obsoleta nella metà posteriore del corpo-spirale.L'apertura è stretta, con un breve seno anale ⁽¹⁾.

Distribuzione: Australia: Eocene – Oligocene – Miocene Medio