Encrinurella insangensis ( Reed, 1906 )

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 : 333-335

Encrinurella insangensis ( Reed, 1906)

Fig. 11

1906 Pliomera insangensis sp. nov.; Reed, p. 74–76, pl. 5, figs 19–25.

1915 Pliomera (Encrinurella) insangensis Reed ; Reed, p. 50–51, pl. 8, figs 15, 16, 18–20; non figs 17, 21.

cf. 1998 Encrinurella sp. ; Fortey & Cocks, fig. 3N.

Material. Lectotype (selected herein): cranidium from Hweyawt, Fig. 11.9 ( Reed, 1906, pl. 5, figs 21,22), GSI 8335. Additional type material: cephalon with hypostome and pygidium from Hweyawt, Fig. 11.10 ( Reed, 1906, pl. 5, figs 19, 23), GSI 8334; pygidium from Insang, Fig. 11.7 ( Reed, 1906, pl. 5, fig. 20), GSI 8336; cranidium from Kunlein, Fig. 11.4 ( Reed, 1906, pl. 5, fig. 24), GSI 8338; partial thorax from Ledet, Fig. 11.8 ( Reed, 1906, pl. 5, fig. 25), GSI 8339.Additional material: cephalic shield from Hweyawt, Fig. 11.1 ( Reed, 1915, pl. 8, fig. 16), GSI 11562; cephalic shield from Man Ngai, Fig. 11.2 ( Reed, 1915, pl. 8, fig. 15), GSI 11561; cephalic shield from Makmongshai, Fig. 11.3 ( Reed, 1915, pl. 8, fig. 18), GSI 11564; 2 pygidia from Man Ngai, Figs 11.5 , 6 ( Reed, 1915, pl. 8, figs 19,20 respectively), GSI 11565, 11566 respectively. All material from the Li-Lu Foramtion (Upper Naungkangyi Beds; Katian) at Hweyawt, Insang, Kunlein, Ledet, Makmongshai, or Man Ngai.

Description. The lectotype is distorted, and even with attempted retrodeformation it is not entirely symmetrical. Undistorted cephalic shield from Reed’s later collection twice as wide as long, with maximum glabellar width across frontal lobe slightly exceeding that across genal area. A good cephalic shield ( Fig. 11.3 ) is somewhat flattened and is relatively slightly wider across the frontal lobe, but there is probably still some transverse extension on this specimen, which also has more divergent axial furrows. The general resemblance between most of the specimens in different preservational states is still sufficient to suggest that one species is involved (but see comments below). Forward expansion of glabella is ten to fifteen degrees as measured to sagittal line on good material. Glabellar furrows short and deep, and with characteristic form: S1 gently concave forwards, S2 transverse or nearly so, while S3 is distinctly convex forwards, apostrophe shaped. Glabellar lobes accordingly vary in shape, with L1 very narrow (exsag.) especially laterally near axial furrow, L2 subrectangular, nearly twice as wide (exsag.) as L1, L3 longer again, more rounded, and appearing slightly inflated. Occipital ring extends laterally as far as, or slightly beyond L1, where it is noticeably narrower than in its median two-thirds. Occipital furrow curves forwards over this part, laterally deepening in line with glabellar furrows. Dorsal furrows are deep, including the axial furrows, but this is because the figured specimens are mostly internal moulds: the cast from the dorsal surface ( Fig. 11.3 ) shows narrower furrows in general. This specimen also shows the posterior cranidial border most faithfully: gently convex, and hardly widening laterally, defined by deep but narrow border furrow. The border furrow is much exaggerated on the internal mould and the border appears narrower and more convex. Prominent semicircular palpebral lobes are located opposite L3 at about one quarter of the transverse width of the adjacent glabella, the eye lobe as a whole standing proud and about one quarter length (exsag.) of glabella in front of occipital ring. Cheeks inside palpebral lobes gently convex, as also behind the eye lobe. Postocular cheek triangular, more or less bisected by the posterior border furrow. Course of facial suture best seen on Fig. 11.10 , showing anterior branch running near to the axial furrow and curving anteriorly closely around the frontal lobe of the glabella, outlining a narrow cranidial border there; posterior branch diverges behind the eye and runs to genal angle. One of Reed’s (1906) specimens ( Fig. 11.10 ) has the glabella broken to reveal the outline of the hypostome beneath. It has a rounded-triangular outline tapering posteriorly and surrounded by a narrow and convex border. There is a suggestion of marginal denticles, especially close to the midline.

The narrow free cheek extends forwards in a spine-like way to form the narrow border in front of the glabella. In dorsal view the wide, outward-sloping lateral cranidial border is dominant, outlined by a deep and wide marginal furrow. The convex eye is elevated on an eye socle which is defined at the base by a furrow running parallel to the border furrow, though half the width. Between this furrow and the border furrow an elevated and convex ridge is parallel to the lateral border. An incomplete thorax of eight segments is plausibly associated ( Fig. 11.8 ) (compare with that of Encrinurella tetrasulcata Ju in Tripp et al., 1989, fig. 14k) showing convex axial rings of equal width having a small anterior forward turn like that on the occipital ring. Very prominent half rings are almost as long (sag.) as the axial rings themselves. Posterior pleural bands of similar width (exsag.) and convexity to axial rings, their outer halves steeply downturned to blunt tips. Anterior pleural bands very narrow (exsag.) depressed below level of posterior bands from which they are separated by transverse furrow extending as far as the pleural articulation. Pygidium has pleural ribs of similar form to thorax anteriorly and is twice as wide long, or somewhat longer; none is perfectly preserved. Four (? five) axial rings of decreasing width and length on gently tapering axis; terminal piece not clearly seen, but presumably very small and triangular. Five pairs of bluntly tipped pleural ribs turned downwards marginally, and progressively posteriorly directed, the rear pair behind the axis and running more or less exsagitally.

Discussion. We are obliged to select a lectotype from the Reed (1906) collection even though less distorted examples are present in the 1915 collection. The cranidium figured here as Fig. 11.9 , original of Reed 1906, pl. 5, fig. 22, is selected, numbered GSI 8335, which has the advantage of an associated pygidium and partial cephalon showing the eye lobe. The type material from Reed (1906) belongs to the single species Encrinurella insangensis , and most of the material he figured in 1915 can be confidently assigned to the same species. However, the internal mould of a cranidium figured here in Fig. 10.5 , original of Reed (1915, pl. 8, fig. 17) differs from that of E. insangensis in several respects, notably in having wider glabellar furrows, smaller L1, and indications of coarse tubercles upon it, which may have been prominent on the dorsal surface. It also shows development of inflated circular lobes at the ends of the occipital ring. These seem to be real features rather than artifacts of preservation. The latter feature may relate to a partial thorax ( Fig. 10.8 ) that also displays inflated lobes at the ends of the thoracic axial rings, with a convex lobe also on the proximal parts of the pleural bands. This thorax clearly belongs to a different species from the thorax of E. insangensis in Fig. 11.8 . These specimens are both excluded from E. insangensis . The cranidium is very tentatively recorded here as Ovalocephalus ? sp. indet.; the thorax may also belong to the same species.

Figures

FIGURE 6. Birmanites birmanicus (Reed) from the Hwe Mawng Beds (uppermost Katian), northern Shan State, Myanmar. 1. Hypostome (original of Reed 1915, pl. 5, fig. 17), GSI 11519, Hwe Mawng. 2a, b. Cephalon (original of Reed 1915, pl. 6, fig. 2), GSI 11522, Hwe Mawng, original and retrodeformation. 3. Partial specimen (original of Reed 1915, pl. 6, fig. 3), GSI 11523, Hpakhi. 4a, b. Pygidium (original of Reed 1915, pl. 6, fig. 4), GSI 11524, Hwe Mawng, original and retrodeformation. 5. Cranidium (original of Reed 1915, pl. 7, fig. 2), GSI 11534, Hpakhi. 6. Partial specimen (original of Reed 1915, pl. 5, figs 15,16), GSI 11518, Hpakhi. Scale bars = 2 mm for 1; = 5 mm for 2–6.

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.

FIGURE 11. Encrinurella insangensis (Reed) from the Li-Lu and Kunlein Formations (Katian), northern Shan State, Myanmar. 1a, b. Cranidium (original of Reed 1915, pl. 8, fig. 16), GSI 11562, Hweyawt, original and retrodeforamtion. 2. Cranidium (original of Reed 1915, pl. 8, fig. 15), GSI 11561, Mân-ngai. 3. Cranidium (original of Reed 1915, pl. 8, fig. 18), GSI 11564, Makmongshai. 4. Cranidium (original of Reed 1906, pl. 5, fig. 24), GSI 8338, Kun-lein. 5. Pygidium (original of Reed 1915, pl. 8, fig. 19), GSI 11565, Mân-ngai. 6. Pygidium (original of Reed 1915, pl. 8, fig. 20), GSI 11566, Mân-ngai. 7. Pygidium (original of Reed 1906, pl. 5, fig. 20), GSI 8336, Insang. 8. Thorax (original of Reed 1906, pl. 5, fig. 25), GSI 8339, Ledet. 9. Cranidium and pygidium (lectotype, original of Reed 1906, pl. 5, figs 21&22), GSI 8335, Hweyawt. 10. Cranidium and pygidium (original of Reed 1906, pl. 5, figs 19 and 23), GSI 8334, Hweyawt. Scale bars = 2 mm.