| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| CP-651 | 14.8 | 0.39 | 0.45 | 0.40 | 0.87 |
| CP-650 | 15.9 | 0.37 | 0.47 | 0.37 | 0.80 |
| RJ-1642 | 18.9 | 0.38 | 0.44 | 0.40 | 0.85 |
| Age | Origin |
|---|---|
|
Grey clay L. lyelli subzone H. benettianus zone Middle Albian |
Brévonnes Aube France |
Description. Small, thick, pyritic ammonite, entirely septate, with an evolute coiling and whorls 20% covered. Its section is circular but slightly depressed. The umbilicus has a rounded wall that gradually rounds to the flank. The inner whorls are ribbed, and there are 21 strong, simple ribs on last whorl. Rursiradiate and slightly convex, they strengthen towards venter and reach their maximum height on the siphon, which is traversed in a straight line at right angle. Thirteen originate on the umbilical wall, and eight shorter ones begin in the inner half of the flanks. The sutures show round saddles with a median incision and rectangular lobes ending in three teeth, with L1 half the width of S. Note: the first quarter of the last whorl is subtly fastigiate on this specimen, but not on the other two.
Remarks. Personal discovery. Kennedy (2004) measured and figured only two specimens from the lyelli zubzone of Aube, with a depressed whorl section, ribbed inner whorls, 26 ribs on last whorl at about 2 cm in diameter, and a suture line with lobes narrower than saddles. Kennedy defines in the same paper another species from the same level, B. flexuosum, with one specimen measured. It has a slightly compressed section, smooth inner whorls, 20 ribs effaced or attenuated on the siphon at about 2 cm, and lobes narrower than saddles (see its entry). The sutures of these two small species are very similar, except for the narrower lobes in flexuosum. CP-650 is therefore close to multicostatum, except for the number of ribs, which corresponds to flexuosum! This difference likely stems from intraspecific variability, not visible on Kennedy's too small number of specimens. The relevant criteria for distinguishing multicostatum would therefore remain the depressed section and the ribbed inner whorls.