Harpes prescheri, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 50-51

Harpes prescheri n. sp.

Plate 9A–I

Diagnosis. Cephalon widest across eyes and glabella is narrow, cone-shaped, rounded anteriorly with suppressed tubercles straddling its crest. Brim width ratio low at around 0.50, brim slightly concave (sag.), becoming gently convex close to posterior border, alar furrows effaced distally, perforations on brim very fine. Prolongations shorter (exsag.) than cephalon (sag.). Pleurae shortening (tr.) posteriorly over last fifteen thoracic segments to become very short, giving pointed appearance to thorax.

Etymology. Named in remembrance of Harald Prescher, a trilobite researcher and a good friend.

Material and occurrence. Holotype: NHMUK It 29244, Pl. 9A–E , from a horizon around 100 m upslope of “Couche Rouge” close to the “ Psychopyge Couche ”, Er Remlia Formation, Emsian, Jbel Issoumour ( Fig. 2B, Map 7, site 9), disarticulated dorsal exoskeleton . Paratype: NHMUK It 29243, Pl. 9F–I , from type horizon and locality ( Fig. 2B, Map 7, site 8), cephalic dorsal exoskeleton .

Other material: H. cf. prescheri, NHMUK It 29245, Pl. 9J–N from the “ Lobopyge Couche ”, El Otfal Formation, Eifelian, Issoumour (see Issoumour section, McKellar & Chatterton 2009, p. 12) ( Fig. 2B, Map 7, site 2).

Description. Cephalon and genicranium narrow, length (sag.) 86% and 76% of width (tr.), respectively. Widest point of cephalon and genicranium of holotype at midpoint between eye lobes and alae and at posterior border, respectively. Glabella narrow, carinate, and with coarse, barely-inflated tubercles on crest. Width (tr.) of glabella at S1 around 65% of length (sag.) of glabella anterior to S0. S1 sloping posteriorly and curving slightly anteriorly, S2 and S3 very shallow, barely rising out of axial furrow. Axial furrows very gently convex and converging anteriorly at more than 150 to sagittal line. Preglabellar furrow shallow and straight (tr.) in anterior view. Occipital furrow deep and straight (tr.). Occipital ring medially broadened and in lateral view, lower than glabella anterior to S0. Occipital node small and barely inflated. L1 not inflated although alae are. Alae large (tr.) and narrow and reaching over 60% of way across genal area. Alar furrow very shallow and distally effaced. No interalar furrows or ridges. Posterior border short (tr.), under 30% of width of occipital ring (tr.).

Genal area narrow, width (tr.) around 50% of length (exsag.) and lacking pits and caeca. Preglabellar genal area narrow (sag.), length (sag.) ≈20% of width (tr.). Eye lobes very large, strongly inflated, cone-shaped and extending to axial furrow. Eye location ratio around 0.83. Two fairly small oval eye lenses ( Pl. 9D ). Genal ridge barely indicated, becoming a little more visible posterolaterally on genal roll. Anterior boss barely inflated and girder weakly kinked. Genal roll gently sloping anteriorly (≈ 45 o) and moderately steeply laterally (≈ 600). Perforations on genal roll about same size as those on brim, becoming slightly smaller away from girder. Row of large perforations immediately above girder, and at inner margin of fringe, anterior to glabella, row of perforations a little larger than those on main part of genal roll.

Brim wide, about one third of cephalic length (sag.), sloping moderately (≈ 170), gently concave anteriorly, straight laterally and becoming gently convex close to posterior border. Brim width ratio just over 0.50. Brim perforations becoming smaller away from girder to become very fine (standardised diameter of ≈80 μm). Row of larger perforations at proximal and distal edges, no caeca. Rim stout and lacking tubercles on dorsal surface. Marginal band near vertical with dorsal surface overhanging. Prolongations moderately long (exsag.) at 85% of cephalic length (sag.). In dorsal view, internal rim curving smoothly adaxially and concave posteriorly in lateral view. Internal rim wide (tr.), wider than external rim (sag.) and with tubercles on dorsal edge. Genal spine short set slightly obliquely adaxially.

Thorax little known but inner portion of pleurae shortening (tr.) strongly posteriorly, much more than axial rings. ( Pl. 9A ). Pygidium and hypostome not known.

Remarks. Harpes prescheri lacks only one of the diagnostic characters for the genus shown in Table 5a, in having a weak girder kink rather than no girder kink.

Harpes prescheri and H. lahceni are similar but have well defined differences. The cephalon, genicranium and glabella of H. prescheri are much narrower, the genal roll is more gently-sloping anteriorly and the brim is wider (sag.) and has a brim width ratio of just over 0.50, whereas that of H. lahceni is 0.76. Also, the dorsal surface of the rim lacks tubercles, and the length (exsag.) of the prolongations expressed as a percentage of cephalic length (sag.) is 82% and 112% for H. prescheri and H. lahceni , respectively. In lateral view, the profile of the internal rim of H. prescheri is concave and not wave-like as it is in H. lahceni .

NHMUK It 29245, designated as Harpes cf. prescheri , ( Pl.9 J–N ) is similar to H. prescheri in having a steep genal roll anteriorly and a short (sag.) preglabellar field, but differs in having a narrower brim (sag.) and a brim width ratio of 0.73 rather than 0.50.

Figures

PLATE 9. A–I Harpes prescheri n. sp., from an horizon 100 m upslope of “Couche Rouge”, close to the Pyschopyge horizon, Er Remlia Formation, Emsian, Jbel Issoumour (Fig. 2B, Map 7). A–E dorsal exoskeleton of cephalon and disarticulated thorax, holotype, NHMUK It 29244 (site 9). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations, E, lateral view of eye lobe (uncoated). F–I dorsal exoskeleton of cephalon, paratype, NHMUK It 29243 (site 8);, F dorsal, G, anterior and H, lateral view. I, dorsal view of brim perforations. J–N Harpes cf. prescheri, dorsal exoskeleton of cephalon, NHMUK It 29245, from “Lobopyge Couche”, El Otfal Formation, Emsian/Eifelian boundary, Jbel Issoumour (Fig. 2B, Map 7, site 2). J, dorsal, K, anterior and L, lateral view. M, lateral view of glabella (uncoated) and N, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.