Ammonite type Eubostrychoceras otsukai (Yabe, 1904) morphe boulei (Collignon, 1932).
Lower Campanian Cretaceous, 83 to 72 million years BC, Menabe region, Madagascar.
On its modern semi-spherical base in light wood, with brass plate.
H. 20 x D. 7.5 cm. H. 29 cm (with base).
- Christie's Paris sale, April 16-17, 2008, lot 89 (sold for €9,250).
- Private collection, France.
The ammonite undergoes a helical growth when it is juvenile and then in adulthood, the last turn goes up in a butt towards the top. The group of E. otsukai is distinguished by its generally loose, corkscrew coil over most of the shell. The early stages could be straight and aligned with the axis of the winding, but not included in the helix. The boulei morphotype has a more or less tight winding, an ornamentation of fine ribs more or less dense, straight, annular, simple, tightening without fading when crossing the dorsal wall. Constrictions are very rare or absent. The umbilicus is very open.