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Aphelaeceras arkansanum
Taxonomy
Aphelaeceras arkansanum was named by Gordon (1964). Its type specimen is USNM 119700, a shell, and it is a 3D body fossil. Its type locality is USGS 8871, ridge between Tyler and Possum Creeks, which is in an Arnsbergian marine limestone in the Imo Formation of Arkansas.
Synonymy list
| Year | Name and author |
|---|---|
| 1964 | Aphelaeceras arkansanum Gordon p. 148 figs. pl. 11, figs. 14–18, text-fig. 22 |
| 2007 | Aphelaeceras arkansanum Niko and Mapes pp. 294 – 295 fig. 1–2 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Aphelaeceras arkansanum Gordon 1964
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| S. Niko and R. H. Mapes 2007 | Description of juvenile whorl.—Umbilicus perforate with 3.5–4.1 mm and 4.4–5.5 mm short and long diameters, respectively, of umbilical perforation. Apex not preserved, embryonic shell probably cone-shaped; early juvenile whorl, representing the first approximately 2/3 volution, has Stroboceras-like indented whorl sections having concave venter with ventral groove (vg), roughly concave ventrolateral shoulders with three bilaterally symmetrical grooves (v-lg 1, 2, 3), roughly parallel flanks with three bilaterally symmetrical lateral grooves (lg 1, 2, 3) and rounded dorsum; whorl surface is ornamented by longitudinal ridges and transverse lirae; prominent ventral ridges (vr) at boundary between vg and v-lg, ventrolateral ridges at boundary between v-lg 1 and v-lg 2 (v-lr 1, weak), at boundary between v-lg 2 and v-lg 3 (v-lr 2, weak) and at boundary between v-lg and lg (v-lr 3, prominent), lateral ridges at boundary between lg 1 and lg 2 (lr 1, weak), at boundary between lg 2 and lg 3 (lr 2, relatively weak), and weak dorsolateral ridges (d-lr) at boundary between lg 2 and umbilical wall. Surface lirae form deep tongue-shaped ventral (hyponomic) sinus, weak ventrolateral saddles, relatively shallow lateral (ocular) sinus and nearly transverse dorsal rim; some lirae indicate intermission or bifurcation on flanks. There are three series of discontinuous points, forming weak constrictions of surface lirae; among these, the most adoral discontinuous point occurs at approximately 2.1 mm in the dorsoventral whorl diameter; shell form, terminated by this most adoral discontinuous point, is cyrtoconic with a length of 4.9 mm (apex missing). |