Conus concavus                                    (Lyell & Sowerby in Lyell, 1840)          

Conacteon (Euconacteon) concavus     (Fischer & Weber,  1997)

Classe               Gastropoda                 (Cuvier, 1797)

Sottoclasse        Orthogastropoda        (Ponder & Lindberg, 1996)

Superordine       Heterobranchia           (J. E. Gray, 1840)

Ordine               Opisthobranchia         (Milne-Edwards, 1848)

Descrizione e caratteristiche:

The oldest fossils described as Conus are from the Lias of Normandy near Caen; they are of Pliensbachian age (188-196 mybp; absolute dates in this paper are taken from Harland et al., 1982, and Haq & Van Eysinga, 1987) ⁽¹⁾.

Charles Lyell read an informal account  of the discovery of these specimens in a publication of the Linnaean Society of Normandy ([Eudes-Deslongchamps], 1837). He collected

at the site in 1840, and later that year (Lyell,1840), in collaboration with G. B. Sowerby, he described Conus cadonensis and Conus concavus ⁽¹⁾.

Deshayes & Milne Edwards (1845:7) questioned the assignment of these species to Conus, and soon d'Orbigny (1850, 1852) confirmed their suspicion by demonstrating in sectioned specimens that the last whorls are thin and that internal shell walls are not resorbed.

In Conus, the last whorl is thick and inner walls are often reduced to 50 μm (Kohn et al., 1979), in Eocene as well as modern species (Kohn, 1982).

Bibliografia Consultata

• (1) - Alan J. Kohn “Tempo and mode of evolution in conidae” – Malacologia 1990, 32(1): 55-67

• (2) - Lyell C., 1840 - On the occurence of species of shells of the genus Conus in the Lias, or inferior Oolite, near Caen in Normandy. Annals and Magazine of Natural History, vol. 6, p. 292-296 (publié en décembre)

• (3) - Fischer (J.-C.) & Weber (C.), 1997 - Révision critique de la Paléontologie française d'Alcide d'Orbigny. Volume 2: Gastropodes jurassiques, p. 7-300 (publié en janvier)