| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| CP-567 | 33 | 0.43 | 0.44 | 0.23 | 0.98 |
| BM LFS 437 | 45 | 0.40 | 0.42 | 0.35 | 0.95 |
| Holotype | 68 | 0.41 | 0.38 | 0.30 | 1.08 |
| Age | Origin |
|---|---|
|
Base of bed VII, biplicatus zone, Middle Albian |
Folkestone, Kent Angleterre |
| Var. | glaber | chloris | tethydis | biplicatus | parkinsoni |
|---|---|---|---|---|---|
| H/T | 1.85-2.10 | 1.41-1.63 | 1.09-1.45 | 0.95-1.08 | 0.95-1.00 |
| T/D | 0.23-0.26 | 0.30-0.32 | 0.33-0.42 | 0.36-0.42 | 0.43-0.44 |
Description. Pyritic specimen without visible sutures, with a pearly test and whorls 50% covered. Slightly compressed, hexagonal whorl section with flattened flanks converging towards a flat venter, becoming slightly concave at the end of the spire. Umbilicus sloping at 40°, the edge of which bears 10 radially pinched bullae, progressively stronger and more prominent. Each bulla gives rise to a bundle of 2 or 3 proverse ribs. Most are lautiform, but some are zigzagging. These ribs terminate in 31 small, rounded ventrolateral clavi, alternating on either side of the siphon. These clavi give the impression of a slightly concave venter, but in fact, the venter is flat if traversed along an intercostal space. The angle of incidence of the clavi with the siphon is 40°, but it decreases over the last quarter of whorl.
Remarks. This is a surprising specimen because the ribs are not lautiform on the unexposed side. Dimorphoplites doris Spath, 1926, has irregularly lautiform ribs, but on each flank. Furthermore, it does not extend to bed VII. The last table, based on the specimens of Spath (1926), compares the Dimorphoplites with lautiform ribs, from the most compressed to the thickest. According to Amédro (1992), all are variants of D. biplicatus, which has anteriority. The H/T ratio of our ammonite corresponds to D. biplicatus sensu stricto. Two other specimens can be seen in Hadland (2018) and on Jim Craig's website. Young et al. (2010) illustrate a specimen of D. tethydis. Craig's specimen, with its H/T ratio of 1.16 (measured on the photos), is actually closer to this latter variant.