Hibbertia aodiensis, Lee, 2013

Lee, Dong-Chan, 2013, Late Ordovician trilobites from the Xiazhen Formation in Zhuzhai, Jiangxi Province, China, Acta Palaeontologica Polonica 58 (4), pp. 855-882 : 866-868

Hibbertia aodiensis sp. nov.

Figs. 3B , 7A–D, F, G.

Etymology: After Aodi, a small village next to Zhuzhai.

Holotype: NIGP−152011, incomplete cephalon from locality 2.

Type locality: Locality 2, about 60 m northwest of Zhuzhai, Yushan County. GPS coordinate is 28 ° 34’23.27” N and 118 ° 20’16.50” E .

Type horizon: Xiazhen Formation, Upper Ordovician, Dicellograptus complexus Graptolite Zone.

Material.—Four cephala and one hypostome (repository numbers: NIGP−152008–152013).

Diagnosis.—Species of Hibbertia with a longer (sag.) glabella, brim that is narrow, deep, flat−bottomed, and lower−leveled ala, and lacking interalar furrow.

Description.—Cephalon minus prolongation semi−circular in outline; cephalic and prolongation length nearly equal. External rim strongly vaulted. Brim narrow, deep and nearly flat−bottomed; sagittal length about one−fifth of cephalic length. Genal roll slightly convex outwards and steeply down−sloping. Girder deeply impressed and extends to mid−point of prolongation. Girder kink weakly developed. Inner margin of fringe runs parallel to genal roll and then strongly curved inwards to merge into internal rim; the margin expressed by moderately raised ridge which corresponds to distal limit of caeca on genal area. Anterior boss and preglabellar depression absent. Transverse preglabellar ridge weakly developed. Glabella strongly vaulted and bulletshaped, with maximal sagittal length being 54% of cephalic length. Axial furrow deep and moderately wide, narrowing forwards. Three pairs of glabellar furrows present; S1 straight, deeply incised and obliquely directed backwards; S2 short and anteriorly directed; S3 short (but longer than S2) and anteriorly directed. L1 convex and sub−triangular in outline. S0 wide and shallow, with deeply impressed distal end; L0 strongly convex, and anterior margin curved forwards; small sagittal node present. Palpebral lobe highly raised. Eye small and located at anterior 35% of glabellar sagittal length; distal end located at the same exsagittal line as that of ala. Eye ridge moderately developed and slightly obliquely directed backwards. Ala semi−circular in outline, moderately convex, and much lower than genal area; maximum width 75% and maximum length 40% of corresponding glabellar dimension. Alar ridge weakly developed, follows axial furrow, and ends immediately posterior to adaxial end of eye ridge. Alar furrow steep−sided, deep and wide, becoming shallower and narrower forwards. Interalar furrow and alar depression absent. Internal rim strongly raised, becomes narrow adaxially, and extends posteriorly to meet external rim.

Brim ornamented with one or two rows of large pits along distal extremity and girder, and anastomosing caeca at bottom; pits along distal extremity larger than those along girder; genal roll with smaller pits (pits become larger towards girder); genal area with anastomosing caeca; glabella with weakly developed caeca along crest (only observed in external mold); pits on brim and genal roll become larger posteriorly; caeca on genal area form distinct ridge that runs anteriorly from proximal end of eye ridge, gently convex outwards, and abruptly stops at inner margin of fringe, and runs posteriorly from palpebral lobe, gently convex outwards, and then smoothly merged into inner margin of fringe.

http://dx.doi.org/10.4202/app.2010.0036

Hypostome as wide as long. Anterior lobe of middle body convex and sub−circular in outline; posterior lobe small and crescentic in outline; sagittal length of posterior lobe 20% of hypostomal sagittal length. Anterior margin gently convex forwards; lateral margin straight at antero−lateral portion, gently curved inwards at mid−point of hypostomal length, projected outwards opposite anterior end of posterior lobe, and then runs straight and obliquely posteriorly; posterior margin slightly curved forwards. Anterior border widens abaxially and narrows to disappear absent adaxially; lateral border rimmed, and of consistent thickness; lateral border furrow moderately deep, but shallows out posteriorly. Middle furrow shallows out adaxially. Macula indistinct.

Thoracic pleura straight with shallow and wide pleural furrow that continues into pleural spine.

Remarks.—Of Hibbertia species ( Ebach and McNamara 2002), Hibbertia aodiensis sp. nov. is similar to H. inghami (= Paraharpes inghami ) ( Owen 1981: pl. 7: 21–24, pl. 8: 1) from Norway. Both share a flat−bottomed brim with largepitted distal and proximal extremities, two caecal ridges on genal area (one that runs anteriorly from proximal end of eye ridge and the other that runs diagonally from palpebral lobe), and the same ornamentation pattern in the brim, genal roll and genal area. However, this new species differs in having a longer (sag.) glabella, narrower (sag.) brim, taller external rim, much distinct inner margin of fringe, taller genal roll, and less elevated ala, and lacking an interalar furrow. Hibbertia ottawaensis (Billings, 1865) from Canada (see Shaw 1968: pl. 6: 18) bears the similar glabellar morphology with regard to its sagittal length. However, it shares such features as elevated ala and interalar furrow with other Hibbertia species, which are not present in H. aodiensis .

Stratigraphic and geographic range.—Late Ordovician and Jiangxi Province, South China.

Figures

Fig. 3. Reconstruction of new species described from the Late Ordovician Xiazhen Formation; all drawings are not to scale. A. Remopleurides xiazhenensis sp. nov., dorsal view of exoskeleton (A1), and dorsal (A2) and ventral (A3) view of thoracic segments; exact extent of thoracic axial spine in A1 is not known and articulating half ring is reconstructed as if the anterior margin is broadly notched (see text for details). B. Hibbertia aodiensis sp. nov., dorsal view of exoskeleton; pits and caeca are omitted. C. Vietnamia yushanensis sp. nov., dorsal view of exoskeleton (C1) and lateral view of thoracic segments (C2); granules (see Fig. 9N) are omitted. D. Ceraurinus zhuzhaiensis sp. nov., dorsal view of exoskeleton; granules (see Fig. 10B1, B3) are omitted. E. Pliomerina tashanensis sp. nov., dorsal view of cranidium.