| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| CP-18 | 67 | 0.40 | 0.39 | 0.34 | 1.04 |
| CP-160 | 78 | 0.40 | 0.39 | 0.33 | 1.03 |
| CP-72 | 87 | 0.43 | 0.40 | 0.32 | 1.07 |
| CP-317 | 123 | 0.35 | 0.36 | 0.36 | 0.98 |
| Holotype | 128 | 0.38 | 0.40 | 0.37 | 0.96 |
| Age | Origin |
|---|---|
|
Lower Albian Malagasy zone of Lemuroceras spathi & Brancoceras besairiei |
Ambarimaninga Boeny Region Madagascar |
Description. A fully septate specimen, with a nearly complete test and 50% covered whorls. The last quarter of whorl is slightly crushed: in fact, the cross-section is broad and U-shaped, with a broadly rounded venter and flattened, slightly convergent flanks. The umbilicus is broad, with a subvertical wall, joining the flanks by a rounded edge. Six thin, shallow sigmoid constrictions per whorl originate on the curve of the umbilical edge and cross venter, forming an angular proverse sinus at 120-130°. These are preceded by a collar (like a thickened rib), originating at mid-flank and widening on venter. Quite often, another ridge follows each constriction on the inner half of the flanks. The ribs begin threadlike near umbilicus, then thicken, and some bifurcate. Taking into account some intercalated ribs of unequal lengths, there are 14 to 18 ventral ribs between two constrictions. The internal mold shows attenuated ribs but more pronounced constrictions.
Remarks. Beyond 10 cm, the constrictions become straight, the ventral sinus becomes rounded, the ridge after each constriction disappears while the collar before thickens and extends down to the umbilical margin. This species is long-lived, having also been found in the Upper Albian of Venezuela (Renz, 1972, 1982) and Alicante in Spain (Cremades & Linares, 1982). We note two details not mentioned in the literature. The first is that the constrictions are almost strangled as they pass the siphonal line, on the internal mold. The second is that the ribs are slightly more sinuous than the constrictions. Consequently, the rib after a constriction often moves away from it slightly, then returns to it midway along the flank, while the rib before a constriction detaches from around mid-flank.