Cleoniceras (Cleoniceras) cleon  (d'Orbigny, 1841)

Measurements	D mm	H/D	T/D	O/D	H/T
CP-85	36.1	0.53	0.27	0.14	1.99
5769-1 MNHN lectotype	69.9	0.53	0.28	0.11	1.90

Age	Origin
Grey clay O. subhilli zone Lower Albian	Mesnil-Saint-Père Aube France

Description. Small pyritic internal mold, fully septate, with well exposed sutures. Discoidal ammonite, highly compressed and involute, with whorls 85% covered. Very high ogival whorl section, with slightly convex flanks and a very narrow, arched venter. Maximum thickness is reached in the lower third of the flanks. Umbilicus small but clearly revealing the internal whorls, with a low, vertical wall and a rounded rim bearing nine radially pinched umbilical bullae. The ribs are weak and sigmoid. Each bulla gives rise to a convex, proverse primary rib, which divides into two secondary ribs looking like concave crescents projecting forward near venter. The primary ribs are initially very short, then their point of bifurcation gradually rises to mid-flank. Some secondary ribs divide in turn. A shorter intercalary rib is often inserted between two consecutive pairs. We can barely count 22 ribs in total, effaced on the narrow venter.

Remarks. Personal discovery. A readily recognizable ammonite, very similar to the lectotype reproduced in Casey (1966, p. 556) and Fischer (2006, pl. 34, fig. 1a-b). In particular, the suture is very typical: S, S1, and L are broad and moderately elevated, L is highly asymmetrical, while the auxiliary elements are collapsed in comparison. This young specimen still has a narrow rounded venter. On larger specimens, it becomes sharp, the umbilical margin is angular, and the whorl section rises further. Finally, the ribs and umbilical bullae disappear. In the Aube region of France, this uncommon species has been found in the floridum, puzosianus, and subhilli zones (Matrion in Colleté, 2010). It is rare in England, which has yielded only a few incomplete specimens.