Prionocheilus liluensis ( Reed, 1915 )

Fortey, Richard A., Wernette, Shelly J. & Hughes, Nigel C., 2022, Revision of F. R. C. Reed’s Ordovician trilobite types from Myanmar (Burma) and western Yunnan Province, China, Zootaxa 5162 (4), pp. 301-356 : 336

Prionocheilus liluensis ( Reed, 1915)

Fig. 10.9

1915 Calymene (Pharostoma) liluensis ; Reed, p. 4647, pl. 8, figs 6, 7, non pl. 8, fig. 9.

Material. Holotype. Cranidium GSI 11554. Reed (1915, p. 47) did not associate the pygidium he figured with confidence, and it is therefore not to be regarded as one of the type series. Since this pygidium is that of an Ovalocephalus sp. (above) the cranidium is the only type specimen available for holotype. Reed illustrated part and counterpart of this specimen. Upper Naugkangyi Beds (Katian). Lilu right bank of Nam Tu , path to Manping. northern Shan State.

Description. The external mould of the holotype is illustrated herein, and is reasonably well-preserved, although the tip of the fixed cheek is not present. Glabella occupies three-quarters of cranidial length (excluding occipital ring), and is as wide as long; occipital ring 25% total glabellar length. Glabella best preserved on right side showing convex flanks narrowing forwards to broadly arcuate front. Deep S1 with outer end at three-eighths cranidial length, curving inwards but fading well before occipital furrow, distally not quite becoming exsag. S2 follows in line with inner part of S1, and shallower, its anterior termination just behind a prominent anterior pit at the end of the axial furrow. L1 is twice as wide and twice as long as L2, and both somewhat inflated. Occipital ring well defined, narrows laterally, and carries a prominent circular median tubercle. Preglabellar field as wide (sag.) as border in front near midline, and widens towards corner of glabella. Palpebral lobe situated about 40% of the distance across the adjacent glabella, and of similar length (exsag.) to preglabellar field (sag.). Eye ridges strong and convex, directed back at about 60 degrees to sag. line.Anterior border furrow of even, moderate depth along its length. Border hardly convex and gently bowed forwards. Posterior border furrow as deep as axial furrows, and posterior section of fixed cheek presumably broadly triangular. Facial sutures diverge at a low angle in a convex curve in front of the palpebral lobes and at a high angle behind. Much of the dorsal surface is covered by fine tubercles, which appear coarser and sparser immediately in front of the preglabellar furrow and on the postocular fixed cheeks. A cranidium described by Kolobova (in Sokolov & Yolkin,1978, pl. 27, fig. 7) under the name Pharostoma inermis from the Upper Ordovician of Tien Shan is very like that of Prionocheilus liluensis , although it apparently has coarser tubercles on the dorsal surface.

Figures

FIGURE 10. (1, 2) Lonchodamas? sp. (Reed) from the Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. 1a, b. Pygidium (original of Reed 1915, pl. 5, fig. 6), GSI 11508, original and retrodeformation. 2. Cranidium (refigured from Reed 1915, pl. 5, fig. 5), GSI 11507. (3, 6) Lonchodamas shanensis (Reed) from the Hwe Mawng Beds (uppermost Katian), northern Shan State, Myanmar. 3. Pygidium (original of Reed 1915, pl. 5, fig. 3), GSI 11505, Hwe-hok. 6. Cranidium (original of Reed 1915, pl. 5, fig. 2), GSI 11504, Mong Ha. (4) Dionide hybrida (Reed), Cephalon (original of Reed 1915, pl. 5, fig. 7), GSI 11509, Hwe Mawng Beds (uppermost Katian), Hwe-hok, northern Shan State, Myanmar. (5, 8) Ovalocephalus? sp. indet. (Reed) from the Li-Lu Formation (Katian), Mân-ngai, northern part of Shan State, Myanmar. 5. Cranidium (original of Reed 1915, pl. 8, fig. 17), GSI 11563. 8. Thorax (original of Reed 1915, pl. 8, fig. 21), GSI 11567. (7) Pliomerina martellii (Reed), Cranidium (original of Reed 1917, pl. 8, fig. 15), GSI 11915, Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. (9) Prionocheilus liluensis (Reed), Cranidium (original of Reed 1915, pl. 8 figs 6 and 7), GSI 11554, Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. (10, 13) Ovalocephalus sp. (Reed) from the Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. 10. Pygidium (original of Reed 1915, pl. 8, fig. 9), GSI 11556. 13. Cephalon; not previously figured; no GSI catalogue number. (11, 12) “Calymene” oldhami (Reed) from Lower Naungkangyi Beds (probable Darriwilian), Mâ Shio, northern Shan State, Myanmar. 11. Cephalon and thorax (original of Reed 1915, pl. 8, fig. 11), GSI 11558. 12. Cephalon and partial thorax (original of Reed 1915, pl. 8, fig. 10), GSI 11557. Scale bars = 2 mm for 1–3, 6, 8–13; = 5 mm for 4, 5; = 1 mm for 7.