Leptellina sp.

Zhan, Renbin & Jin, Jisuo, 2005, Brachiopods from the Middle Ordovician Shihtzupu Formation of Yunnan Province, China, Acta Palaeontologica Polonica 50 (2), pp. 365-393 : 380-384

Leptellina sp.

Fig. 11D–J; Table 9.

Material.—Five ventral internal, and three dorsal internal and two external moulds.

Diagnosis.—Similar to L. spatiosa sp. nov., but subcircular in outline. Ventral muscle field subtriangular to subpentagonal; two trunks of vascula media long, parallel; pair of crescent−shaped knobs near mid−length of ventral valve. Dorsal valve gently concave with short, sharp geniculation.

Description.—Shell medium−sized, concavoconvex, subcircular, with maximum width along hinge line. Cardinal extremities rounded to subrectangular. Ventral valve nearly three−quarters as long as wide; interarea apsacline, about one−seventh of shell length; delthyrium narrow, covered by arched pseudodeltidium. Visceral area of dorsal valve gently concave; geniculation short, sharp; dorsal interarea low, planar, hypercline, less than one−tenth of shell length. Unequal parvicostellae.

Teeth stout, projecting anteriorly from hingeline as wedge−shaped knobs, with crenulated upper surfaces; dental plates absent; muscle field deeply impressed, subtriangular to subpentagonal, about one−quarter length and width of shell; adductor scars triangular, elevated, flanked by elongate diductor scars; mantle canal system saccate (Fig.

+ Fig. 11. A–C. Leptellina spatiosa sp. nov. A. NIGP139117 , paratype, dorsal internal mould (A 1) and latex cast (A 2). B . NIGP139118 , paratype, dorsal internal mould. C . NIGP139119 , paratype, dorsal external mould. D–J. Leptellina sp. D . NIGP139120 , ventral internal mould. E . NIGP139121 , ventral internal mould. F . NIGP139122 , ventral internal mould (F 1) and latex cast (F 2). G . NIGP139123 , ventral internal mould. H . NIGP139124 , dorsal internal mould .

I. NIGP 139125, dorsal internal mould. J. NIGP 139126, dorsal external mould. K–N. Leptellinidae gen. et sp. nov. (to be erected by Zhan and Jin in press).

K. NIGP139127, ventral internal (K 1) and external (K 2) moulds. L. NIGP139128, dorsal internal mould. M. NIGP139129, ventral internal mould. N.

NIGP139130, ventral internal mould preserved together with a dorsal internal mould of Protoskenidioides weixinensis sp. nov. (top).

11D–F), clearly impressed; vascula media beginning from anterior ends of diductor scars, extending anteriorly parallel to each other for 3–4 mm, then bifurcating in anterior and lateral directions, with each branch producing numerous fine branchlets towards shell margins; vascula genitalia in postero−lateral parts of valve marked by antero−laterally directed ridges and striae. Two cresent or droplet−shaped knobs developed near mid−length of shell, immediately outside main trunks of vascula media (Fig. 11D, F).

Cardinalia about one−eighth length and one−quarter width of shell; cardinal process thick, ridge− or rod−like, projecting ventrally. Inner socket ridges divergent from each other at about 100°, terminating in rod−like processes. Muscle bounding ridges well−developed, comprising two segments on each side, forming bema−like structure; muscle field subelliptical in outline, about two−fifths length and one−third width of shell; posterior pair of adductor scars circular; anterior pair more elongated; median ridge originating immediately anterior of notothyrial platform, highest at anterior part of muscle field, and terminating at junction with anterior margin of platform; margin of platform marked by thick ridge perpendicular to valve floor.

Discussion.— Leptellina sp. from Weixin is similar to L. qianjiangensis (Liang in Liu et al. 1983) in shell outline and convexity, but the latter has weaker muscle bounding ridges in the dorsal valve, a much stronger platform, a bilobed ventral muscle field, and much shorter main trunks of ventral vascula media. The pair of knobs have not been observed in other species of Leptellina , and their morphological function is unknown. Davidsonia Bouchard−Chantereaux, 1849 has a pair of similar structures called “ventral cones” ( Copper 1978, 1996; Havlíček 1967, 1998), which commonly bear spiralial grooves. No such grooves are associated with the knobs of Leptellina sp. The taxonomic position of this species cannot be determined until more specimens become available for studying the intra−population variation, particularly regarding the development of the pair of ventral knobs.

Leptellinidae gen. et sp. nov. (to be erected by Zhan and Jin in press)

Figs. 11K–N, 12A; Table 10.

Material.—Five ventral internal and two external, and two dorsal internal moulds.

Discussion.—Compared to type material from Changning, southeastern Sichuan Province (Zhan and Jin in press), the Weixin shells are more transverse, and have a weaker but longer dorsal median septum (Fig. 11L), and more weakly impressed ventral muscle field without bounding ridges (Fig. 11K 1, M). All the other internal and external characters of the specimens from both localities are identical (see Zhan and Jin in press for detailed description).

Leptellinidae gen. nov. (to be erected by Zhan and Jin in press), sp.

Fig. 12B–D; Table 11.

Material.—Three ventral external, and one dorsal internal moulds.

Description.—Shell small to medium, concavoconvex, subsemicircular, with maximum width along hinge line. Cardinal extremities acute to subrectangular. Anterior commissure rectimarginate. Ventral valve gently convex, deepest around umbo. Dorsal valve unevenly concave with greatest concavity at junction between visceral and marginal area of shell; interarea low, hypercline. Unequal parvicostellae; 7–9 accentuated costae, with fine costellae inserting at 2.5 mm and 5 mm growth stage respectively; 4–5 fine costellae between two adjacent coarse costae or costellae. Concentric fila evenly spaced, about 11–12 per mm.

Cardinalia about one−ninth length and one−fifth width of shell; cardinal process a simple knob, projecting mainly ventrally; sockets small, narrow, deep, open antero−laterally; socket ridges thick, discrete from cardinal process, divergent from each other at about 120°, and terminating as short, rod−like processes. Muscle field slightly elevated, about one−third length and one−quarter width of shell; outer, posterior pair of adductor scars elliptical, with thick, high lateral bounding ridges; inner, anterior pair smaller, subcircular. Median ridge originating between anterior pair of adductor scars, limited to central part of shell. Platform marked by weak, discrete, anteriorly or antero−laterally tilted small septules.

Discussion.—This species differs from Leptellinidae gen. et sp. nov. (to be erected by Zhan and Jin in press) in having a much less transverse and more gently concavoconvex shell. More specimens, particularly ventral valves, are needed for identification to species level.