Deltapliomera inglei, E.B & Adrain & Karim, 2018

E. B, Neo, Adrain, Jonathan M. & Karim, Talia S., 2018, The pliomerid trilobite Ibexaspis and related new genera, with species from the Early Ordovician (Floian; Tulean, Blackhillsian) of the Great Basin, western USA, Zootaxa 4525 (1), pp. 1-152 : 23-25

Deltapliomera inglei n. sp.

Plate 20, Plate 21, figs 1–21

2009 Ibexaspis sp. nov. 3; Adrain et al., p. 567.

Material. Holotype, pygidium, SUI 129565 (Pl. 21, figs 13, 17, 18, 20, 21), and assigned specimens SUI 129553– 129564 , 129566 , from Section H 127.1 m, Fillmore Formation (Tulean; Heckethornia bowiei Zone ), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. After Jon Ingle.

Diagnosis. Densely spaced and coarse granulose sculpture all over cranidium, including LO and posterior border; LO without distinct median node in most large specimens; pygidium with sculpture of very coarse granules or tiny tubercles, blending into smaller granules at tips of pleurae; free tips of pleurae long compared to other species.

Description. Deltapliomera inglei is sufficiently similar to D. humphriesi that it is treated with an extended comparative discussion. Ratios are given for comparison with other species. Its librigenae and thorax are unknown.

Cranidium with sagittal length 106.7% (104.2–109.5%) width across γ, 74.0% (71.8–75.7%) width across δ, 74.0% (70.8–76.0%) width across ε, and 54.8% (54.2–55.9%) maximum width across genal angles; the cranidium of D. inglei is broader and slightly less strongly vaulted (sag., especially tr.), with much coarser and more densely spaced tuberculate sculpture; anterior border slightly narrower and less overhung by glabella; glabella narrower and less elongate, maximum width across L3 91.4% (90.0–93.1%) sagittal length, less strongly anteriorly expanded to L3, L3 smaller; axial furrows slightly broader, more laterally bowed and not anteriorly divergent in course; SO slightly shorter and deeper; genal spine shorter, smaller, and blunter; palpebral lobes slightly narrower, longer, and less posterolaterally angled; interocular fixigenae slightly narrower overall; posterior fixigenae longer and broader, a little less strongly downturned.

Hypostome shorter and narrower overall, with smaller, shorter, narrower, more strongly posteriorly tapered middle body; lateral border broader, particularly at shoulders, and more strongly downturned; posterior border longer, and without median dorsal inflection; hypostome in general with slightly finer sculpture.

Pygidium slightly narrower and shorter, with sagittal length from articulating furrow 45.6% width across anterior pleural band of first segment; more strongly vaulted (sag., tr.); axis relatively longer and narrower, width across first ring 41.2% width across anterior band of first segment, and width across fourth ring 50.0% width across first ring, more convex (sag., tr.); axial rings more strongly independently inflated, shorter and more densely tuberculate, especially medially; no terminal piece; inter-ring furrows shorter and deeper; axial furrows deeper and more strongly anteriorly divergent; pleurae slightly wider, with tubercles extending to edge of pleura; pleural spines slightly longer and thinner, with many more tubercles, especially near tips; doublure of even length and shorter medially than that of D. humphriesi .

Ontogeny. Cranidial ontogenetic changes (cf. Pl. 20, figs 1, 3 and Pl. 21, fig. 1) include overall broadening of the cranidium; fining of the sculpture, particularly on the glabella and LO, and addition of smaller tubercles increasing density of its distribution; anterior expansion of the glabella; slight decrease in glabellar vaulting; inflation of lateral glabellar lobes; lengthening, deepening, and slight adaxial extension of lateral glabellar furrows; slight enlargement of L3 relative to L2; effacement of median LO node to blend in with other LO tubercles; and the genal spine shrinks to a rounded nub.

Hypostomal changes include overall elongation; the middle body also becomes longer and narrower, with a better defined (laterally) middle body furrow; the lateral and posterior border furrows become much shallower; and the lateral and posterior borders widen/lengthen considerably. It also appears that the lateral and posterior border sculpture becomes much more dense and finer, although the border area of the smallest specimen (Pl. 21, fig. 4) is obscured by detritus.

The pygidium of D. inglei is known from only two specimens, but the high size disparity (Pl. 21, fig. 16 is a transitory pygidium with a single thoracic segment attached) demonstrates a number of ontogenetic changes. The pygidium becomes wider overall; the sculpture becomes finer but denser, with more small tubercles intercalated; the inter-ring and furrows between pleural ribs lengthen and shallow slightly; the median axial nodes shrink and blend in with the other tubercles; and the pleural spines splay out anterolaterally with increased space between them.

Discussion. Cranidia of D. heimbergi and D. inglei are very similar, but the latter have a more parallel sided glabella that is less strongly inflated; S3 more deeply incised; the palpebral lobes are more slender overall; the posterior fixigenae are wider; the row of tubercles along posterior margin of LO and posterior borders is composed of much smaller and more subdued tubercles; sculpture is generally coarser with more fine granules interspersed between the tubercles. The hypostomes of D. inglei have much broader lateral and posterior borders, are less posteriorly tapered so that their outline posteriorly is more gently rounded rather than pointed, and generally finer sculpture. A comparison of the librigenae and thorax cannot be made as they are unknown for D. inglei . The largest pygidium of D. inglei is overall longer and wider; with longer more widely splayed pleural spines; longer axis; and much more prominently tuberculate sculpture, especially along the central portion of axis, which possesses prominent clusters of larger tubercles, and along the pleural spines, which also exhibit loose rows of prominent tubercles.

A comparison of D. eppersoni with D. inglei is as follows. Cranidia of D. inglei possess glabellae that are narrower and do not overhang the median portion of the anterior border as seen in D. eppersoni ; the interocular and posterior fixigenae are longer, with the abaxial portion of the posterior fixigenae especially so; the palpebral furrows and sutures are less strongly posteriorly divergent; SO and posterior border furrows are shorter and more deeply incised; the sculpture is much coarser and densely spaced, especially on LO (which is mostly effaced medially in D. eppersoni ). The hypostomes of both species are very similar, but those of D. inglei are less convex, with a more posteriorly tapered middle body that is also narrower. The pygidium of D. inglei possesses larger more prominent tubercles overall with a cluster of prominent tubercles running along the sagittal axis; the pleural spines are more widely splayed with the distal tips directed obliquely and not posteriorly in dorsal view as in D. eppersoni , with the fourth pair of pleural spines much longer in dorsal view; first and second axial rings are slightly pinched out abaxially rather than maintaining a constant length (sag., exsag.).