| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| CP-273 | 26.3 | 0.39 | 0.32 | 0.33 | 1.22 |
| Benavides-Cáceres 1956 | 29.5 | 0.37 | 0.32 | 0.37 | 1.16 |
| RJ-536 | 34.8 (31.1) | 0.41 | 0.35 | 0.38 | 1.16 |
| Holotype | 46.0 | 0.38 | 0.32 | 0.38 | 1.17 |
| Age | Origin |
|---|---|
|
Pariatambo Formation ulrichi Peruvian zone Base of Middle Albian |
Huallanca Ancash Region Peru |
Description. Internal mold somewhat evolute in black shale with remnants of black test. Whorls 40% covered, with a moderately compressed section, looking like a rectangle topped by a semicircle, with indistinct ventral shoulders. Umbilicus broad, with a fairly low wall sloping at 70°, clearly showing the internal whorls and passing to the flank with a rounded edge. 23 simple, sharp, concave, and slightly proverse ribs, with wider spacing, originate at the top of umbilical wall. They strengthen to reach their maximum height on ventral shoulders, where they round off. They cross the venter, spreading and flattening, while forming a broad and weak proverse sinus. The ribs become slightly flexuous at the end of the spiral. No trace of tubercles or sutures.
Remarks. This species does not exceed 5 cm in diameter and never has a fastigiate venter. Its 20-30 rigid ribs, appearing very early and flattened on venter, are characteristic. They may be bifid on the inner whorls. The suture figured by Steinmann (1881) and Benavides-Cáceres (1956) is that of Brancoceras, but without the distinct median incision of the main saddle. The ammonite is reported in Peru (Knechtel, 1947; Benavides-Cáceres, 1956; Robert, 2002), Colombia (Bürgl, 1957), and Venezuela (Renz, 1982). Owen (1971) cited it at Courcelles (Aube, France), but this has never been confirmed. Wright (1996) places it in the Lower Albian, but according to Robert (2002) and Robert et al. (2002), it is found in Peru with Lyelliceras lyelli, at the beginning of the Middle Albian. Kennedy & Klinger (2008) suggest that E. aegoceratoides may be a small, pedomorphic descendant of Prolyelliceras matthewsi (see its entry). It appears after the latter, and the very young of both species are often difficult to distinguish.