| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| Holotype Collignon 1949 | 21 | 0.38 | 0.43 | 0.38 | 0.89 |
| CP-54 | 33 | 0.33 | 0.42 | 0.39 | 0.79 |
| Rodolphe Touch | 36.5 | 0.36 | 0.44 | 0.41 | 0.81 |
| Collignon 1963 | 71 | 0.42 | 0.45 | 0.35 | 1.00 |
| Age | Origin |
|---|---|
|
Lower Albian A. besairiei Malagasy zone |
Ambatolafia Boeny Region Madagascar |
Description. An evolute ammonite with a pearly test, whose whorls with a 40% overlap gradually increase in height. The whorl section is depressed-rectangular, with broadly rounded ventrolateral shoulders. The wide umbilicus clearly exposes the numerous inner whorls, with a low, rounded wall, an initial slope of 80°, and a narrowly rounded margin. The last whorl has eight constrictions originating at the umbilical suture, slightly sigmoid on the flanks. They curve forward on the venter to form a broad, rounded sinus. On the last whorl, a magnifying glass reveals that the fine lirae between the constrictions thicken abruptly on the umbilical seam, giving it a striated appearance from which the species derives its name (see the photograph on the right).
Remarks. A species from the Lower Albian of Madagascar (Collignon, 1949, 1963) and South Africa (Kennedy & Klinger, 1979), characterized by its unusual umbilical suture. Without this detail, it resembles two Aptian species from southeastern France, E. duvali (d'Orbigny, 1841) and E. raspaili Breistroffer, 1947. The former, illustrated in Gérard Thomel's Atlas of Aptian Ammonites, has very pronounced convex constrictions. Those of the latter are fewer, 8 instead of 12.