Hentigia Haas, Hahn, and Hahn, 1980

Fortey, Richard A. & Heward, Alan P., 2015, A new, morphologically diverse Permian trilobite fauna from Oman, Acta Palaeontologica Polonica 60 (1), pp. 201-216 : 204-207

Genus Hentigia Haas, Hahn, and Hahn, 1980

Type species: Hentigia bulbops Haas, Hahn, and Hahn 1980 ; Artinskian (Permian), central Afghanistan, original designation .

Discussion.—The genus Hentigia was established to include two species from the early Permian of Afghanistan. Several specimens of the type species show tubercles on the posterior part of the composite anterior glabellar lobe ( Haas et al. 1980: pl. 1: 4, pl. 2: 2). A species from Oman displays remarkably coarse glabellar tuberculation, which we regard as a further expression of the same feature. It is also variably developed from one specimen to another, and often does not extend on to the antero-median part of the glabella over an area probably corresponding with part of the middle body of the hypostome on the venter. The trilobite fauna from Oman is possibly younger than that from Afghanistan, and the coarse sculpture might be regarded as a deriveded character relative to H. bulbops .

Hentigia ornata sp. nov.

Fig. 2.

Etymology: Referring to elaborate cephalic sculpture. Type material: Holotype: well preserved nearly entire exoskeleton, NHMUKPI It 29079. Paratypes: enrolled exoskeletons, NHMUKPI It 29077, 29081–29084, 29137, 29138 (unfigured); cephalic shield, NHMUKPI It 29078, 29080.

Type horizon: Kungurian–Roadian (Permian).

Type locality: Allochthonous limestone, Wadi Khawr al Jaramah, Oman .

Diagnosis.— Hentigia with coarse, but low tubercles on much of the glabella; basal glabellar lobes expand outwards forwards. Pygidium with about 20 axial rings and 9–10 pleural ribs, the first carrying strong adaxial knob.

Description.—Trilobite is 1–1.5 cm diameter when encapsulated, when pygidial margin extends beyond cephalic shield. Posterior part of glabella is not much higher than eyes, more convex anteriorly. Glabella in dorsal view length (sag.) 1.42–1.47 times maximum width across anterior lobe, which is 1.27–1.36 times transverse width of occipital ring. Swollen front part of glabella has an almost perfectly circular outline. Posterior part comprises occipital ring and transverse basal median lobe of similar length (sag.), the latter tapering forwards. Both are well defined by deep occipital furrow and S1. Basal lateral glabellar lobes are inflated, and extend well forwards from median lobe where they slope outwards towards the eyes. Their outline varies from comma-shaped to triangular. They are set off from the composite anterior glabellar lobe by a deep furrow, which however includes a small, subtransverse inflated ridge in some specimens. The anterior glabellar furrows are little more than furrows separating particularly inflated, flattened tubercles representing lobes L2–4. This arrangement is best illustrated on a small cephalon (Fig. 2B) displaying less developed tuberculation, showing three pairs short, forwardly inclined glabellar furrows, the outer ends of the most anterior being opposite the front of the eyes. The expression of the glabellar lobes varies from prominent and inflated, to relatively subdued. On the most tuberculate examples the lobes themselves carry further tubercles, as do the basal and lateral glabellar lobes. The tubercles extend towards the axial line, but do not quite reach it, or become very subdued antero-medially; again, this is variable. Usually prominent median tubercle on occipital ring, where the latter is widest. Axial and preglabellar furrows uniformly deep. Elevated semicircular palpebral lobes about one-third (exsag.) dorsal glabellar length, may be wrinkled or feebly tuberculate. Facial sutures of usual proetoid form outlining spine-like postocular cheeks that essentially comprise somewhat more than half the proximal part of posterior border. Anteriorly divergent sections track the outline of the frontal glabellar lobe until converging across vertical part of anterior border, bending ventrally, and then becoming transverse as rostral suture to meet at midline. The cranidial border narrows medially but is still visible in dorsal view, although the major part of it is bent down vertically. Here it abuts the large transverse rostral plate (Fig. 2F) that carries a pair of inflated bosses at its outer edge.

Free cheek lacks genal spine, genal corner rounded to almost rectangular in dorsal view. Posterior border widens laterally, and curves backwards, adaxially to nick point where cut by facial suture. Lateral border mostly comprises a steep, near vertical wall; it narrows towards the genal angle. Genal field is narrow (tr.) such that on many specimens it is anteriorly no wider than the very prominent eye socle at its widest, and equally inflated there, but posteriorly less so. It may carry weak tubercles adjacent to the deep furrow outlining the base of the eye socle, which is prominent, convex, widest medially. The base of the eye is also marked by a deep furrow, which is narrower than that at the base of the socle. Visual surface is twice as long as high in lateral view. Genal doublure reflexed up to border furrow making a marginal tube around cephalon. Vertical part of genal border carries sculpture of fine raised lines parallel to margin.

Thorax has nine segments of usual proetoid type with preannular half rings visible in enrolled specimens. Pleural tips flatten out distally. Long narrow axial rings may be slightly tuberculate. The tips of the first three segments are concealed beneath the edge of the free cheek during enrolment. In this case, the telescoped parts of the posterior six segments remain visible in lateral view, with just the tips tucked under the cheek edge. This area is backed by a wider plate of doublure.

Pygidium 0.75–0.80 times as long as wide, surrounded by well-defined and convex border with almost circular cross section. Ten pleural ribs are defined by deep furrows, and they are not further subdivided; the tenth rib could be regard- ed as no more than a triangular inflated area. The anterior rib runs into the border, from which the posterior ribs are separated by a deep border furrow. Proximally it carries an extraordinary boss or knob, which marks the point at which the wide facet ends, it can be large enough to overhang the rib behind. This knob appears to be a feature of later ontogeny as it is more subdued on the smallest enrolled specimen (Fig. 2E). Axis occupies no more than 0.4 maximum pygidial width at front of pygidium and tapers to border furrow, but more strongly after the fourth or fifth ring. On most specimens there are seventeen or eighteen rings, of which the first six are more convex (tr.) and clearly defined than those that follow. It has been remarked before (e.g., Lerosoy-Aubril and Angiolini 2009) that the proximal convexity of the axis in these Permian trilobites continues the curve of the thoracic axis as seen during enrolment, such that the maximum axial transverse convexity is at the third ring, not anteriorly as in most trilobites. Depressed lateral areas marking muscle insertion run along the lateral margins of the axis almost to the tip. Narrow ring furrows extend as far as this area.

Discussion.— Hentigia bulbops Haas, Hahn, and Hahn, 1980 , from Afghanistan shares many features with H. ornata , differing obviously in its wedge shaped, rather than spherical anterior part of the glabella; although it has a tuberculate glabella, this is much less coarse than in the species from Oman. The basal glabellar lobes in H. bulbops taper forwards or at most expand very slightly, whereas in H. ornata they frequently push into the palpebral area. The pygidium of H. bulbops lacks the peculiar anterior pair of bosses seen in the new species, although its anterior rib pair is particularly prominent. Glabellar shape in H. planops Haas, Hahn and Hahn, 1980 , is more like that of H. ornata , but its surface sculpture is even more subdued than that of H. bulbops , and it has also less curved palebral lobes and a longer eye than H. ornata , underlain by a much lower, less well defined eye socle.

Genus Iranaspidion Kobayashi and Hamada, 1978

Type species: Iranaspidion sagittalis Kobayashi and Hamada, 1978 ; Guadaloupian (Permian), central Iran .

Discussion.— Iranaspidion is close to Ditomopyge and Pseudophillipsia as Kobayashi and Hamada (1978: 157) recognised, and it may not survive a critical analysis of ditomopygine phylogeny. In reviews of Permian genera Owens (1983, 2003) cautiously retained it, noting its similarity to Pseudophillipsia (Carniphillipsia) particularly. A new species from Oman serves to further reduce the distinction between these various taxa. Like the type species of Iranaspidion it possesses a shallow, but distinctive median furrow or sulcus at the posterior end of the composite anterior glabellar lobe in front of a deep S1, but it lacks the transversely divided basal lateral glabellar lobes included by Owens (1983) as a character of Iranaspidion ; it is more like Ditomopyge in this character. The development of the two nodes on L 1 in the type species is, however, variable, being less on the holotype than on another specimen figured by Kobayashi and Hamada (1978: fig. 1a). However, since it is possible that the posteromedian sulcus is a synapomorphy of I. sagittalis and I. elephas sp. nov. it does potentially have generic significance. It is not present on the type species of Pseudophillipsia (Carniphillipsia) , P. ogivalis Gauri, 1965 . For the moment we employ Iranaspidion as the genus to receive the new species, while noting the reservations expressed by Owens (1983).