Aulacostephanidae SPATH, 1924






Family Aulacostephanidae

Aulacostephanidae are distinguished from Periphinctidae by their ornamentation made up of thickened primary ribs or periumbilicale bullae and secondary ribs of perisphinctid type. The species announced in the "Marls of St Doulchard" are : Aulacostephanus, Rasenia, Eurasenia, Rasenioides...

A. (Aulacostephanoides) attenuatus (Ziegler) M Ø 254 mm
A. (Aulacostephanus) eudoxus (d'Orb.) M, inner whorls Ø 48 mm

Genus Aulacostephanus

Probably coming from the line Liosphinctes - Decipia - Ringsteadia - Pictonia - Rasenia - Rasenioides, the genus Aulacostephanus gathers together ammonites characterized by the presence of a ventral furrow, nonexistent by the genus Rasenia . Aulacostephanoides, Aulocastephanites and Pararasenia are sub-genera.

A. (Pararasenia) hibridus (Ziegler) M Ø 212 mm
A. (Aulacostephanus) pseudomutabilis
(de Loriol) M Ø 127 mm

Genus Rasenia

The macroconch shell (> 250mm) has more or less evolute coiling and oval-shaped whorls. Its ornamentation is made up of relatively long primary ribs, swollen or in form of bullae. 3-5 secondary ribs cross the venter without interruption. The ribbing is flexuous on the inner whorls, but fades on the body chamber.

The microconch form (<40mm) is relatively evolute with subcircular or oval whorl section. Inner whorls have tubercles (bullae), but outer whorls strongly differentiated (perisphinctid) ribbing which persists on the body chamber.

Aperture with lappets

Rasenia gr. evoluta (Spath) M Ø 77 mm, inner whorls
A.(Pararasenia) quenstedti (Durand) M Ø 420 mm