Microcheilinella archensis, Casier & Olempska, 2008

Casier, Jean-Georges & Olempska, Ewa, 2008, Early Frasnian ostracods from the Arche quarry (Dinant Synclinorium, Belgium) and the Palmatolepis punctata Isotopic Event, Acta Palaeontologica Polonica 53 (4), pp. 635-646 : 640

Microcheilinella archensis sp. nov.

Fig. 4F–J .

Etymology: After type locality.

Holotype: IRScNB n° b5077. Carapace. AR−06−27. Fig. 4G. L = 0.81 mm; H = 0.48 mm; W = 0.54 mm.

Type locality: Access path to the Arche quarry.

Type horizon: Chalon Member of the Moulin Liénaux Formation, Early Frasnian, Devonian.

Diagnosis.—Wide Microcheilinella , very asymmetric, especially in the postero−ventral sector. Thin crest parallel to the margin in the postero−ventral sector of the left valve and more rarely of the right valve.

Material.—71 valves and carapaces (samples AR−06−20?, 22, 23, 25–28).

Description.—Relatively large species of Microcheilinella ; wider than high. Ventral and dorsal borders straight or very slightly convex. Anterior and posterior borders angular with the anterior extremity at third−height, and posterior extremity at mid−height. Antero−dorsal, postero−ventral, and posterodorsal margins straight or slightly convex. Antero−ventral margin convex. Greatest height slightly before mid−length, and greatest length at half height. The left valve is larger than the right but their contours are similar. In right lateral view, the left valve projects greatly all along the free margin and the dorsal border, especially in the postero−ventral sector. In that sector, the projection is related to the presence of a thin crest parallel to the margin. Another more reduced crest also parallel to the free margin may be present in the postero−ventral sector of the right valve ( Fig. 4I ). Carapace biconvex in dorsal view except for the pinched extremities. The greatest width is located slightly behind the mid−length. The hinge line is straight, in a depression, and measures almost half the length. In anterior view the carapace is hearth−shaped. The surface of valves is smooth.

Remarks.—In right lateral view, the magnitude of the projection of the left valve in the postero−ventral sector distinguishes M. archensis from all the other species belonging to that genus. The species is known presently only from the type locality.

Figures

Fig. 4. Early Frasnian ostracods from the access path to the Arche quarry, Dinant Synclinorium, Belgium. A. Jenningsina lethiersi Becker, 1971. Poorly preserved carapace in right lateral view. Sample AR−06−26. IRScNB n° b5071. B. Favulella lecomptei Becker, 1971. Carapace in right (B1) and dorsal (B2) views. Sample AR−06−26. IRScNB n° b5072. C. Bairdiocypris sp. 5 sensu Magne (1964). Poorly preserved carapace in right (C) and ventral (C) views. Sample 1 2 AR−06−17. IRScNB n° b5073. D, E. Bairdiocypris sp. C. D. Broken carapace in right lateral view. Sample AR−06−26.IRScNB n° b5074. E. Broken carapace in dorsal view. Sample AR−06−26. IRScNB n° b5075. F–J. Microcheilinella archensis sp. nov. F. Carapace in right lateral (F) and dorsal (F) views. Sample 1 2 AR−06−26. IRScNB n° b5076. G. Holotype. Carapace in right lateral view. Sample AR−06−27. IRScNB n° b5077. H. Carapace in right lateral view. Sample AR−06−28. IRScNB n° b5078. I. Ventral view of a carapace. Sample AR−06−27. IRScNB n° b5079. J. Anterior (J) and posterior (J) views of a carapace. Sam1 2 ple AR−06−28. IRScNB n° b5080. K. Healdianella? sp. B in Becker (1971). Carapace in right (K) and dorsal (K) views. Sample AR−06−28.IRScNB n° b5081. 1 2 L. Bairdia (Rectobairdia) paffrathensis Kummerow, 1953.Poorly preserved carapace in right lateral view. Sample AR−06−23.IRScNB n° b5082. M–O. Bairdia (Rectobairdia) chalonensis sp. nov. M. Holotype. Carapace in right lateral (M) and dorsal (M) views. Sample AR−06−23. IRScNB n° b5083. N. Carapace in 1 2 right lateral view. Sample AR−06−26. IRScNB n° b5084. O. Carapace in right lateral view. Sample AR−06−26. IRScNB n° b5085. Scale bars 200 µm.