内蒙古二连盆地西部早白垩世介形类

EARLY CRETACEOUS OSTRACODA FROM THE WESTERN EREN BASIN, NEI MONGOL

本文记述了内蒙古二连盆地西部白音查干凹陷石油钻孔中发现的介形类化石共6属21种,其中1新属、10新种、2未定种。这是一个以Prolimnocythere,Limnocypridea和Paralimnocythere gen.nov.为优势属的介形类动物群,为国内首次发现,其地质时代为早白垩世。这一介形类动物群的发现,为白音查干凹陷地层的划分和对比及沉积环境的研究提供了古生物依据。

The present paper deals with the ostracods from the western Eren Basin of Nei Mongol. All the samples under study were collected from boreholes. Here described and illustrated are 21 species in 6 genera including 10 new species and 1 new genus, namely, Prolimnocythere neimongolensis sp. nov., P. chuanjingensis sp. nov., Paralimnocythere impolita gen. et sp. nov., P. erenhotensis gen. et sp. nov., P. spinisalata gen. et sp. nov., Cypridea (Cypridea) trita L(?)bimova, C. (C.) sp., C. (C.) paraunicostata Zhang, Cypridea (Yumenia) subremota sp. nov., C. (Y.) binoda sp. nov., C. (Y.) suboriformis Hou, Cypridea (Ulwellia) inandita sp. nov., Cypridea (Pseudocypridina) ellipselloides Hou, LimnocyPridea minuta sp. nov., L. diwopuensis Qi, L. symmetrica Qi, L. trapezoidea sp. nov., L. glaber (Su), Lycopterocypris infantilis L(?)bimova, L. debilis L(?)bimova and Darwinula sp. This ostracode assemblage suggests an Early Cretaceous age.Description of new genus and new speciesFamily Limnocytheridae Klie, 1938Genus Prolimnocythere Song et Cheng, 1982Prolimnoicythere chuanjingensis sp. nov. (P1. Ⅰ, figs. 1—4)Holotype Cat. No. 87001, a complete carapace.Dimensions Length 0.54mm, height 0.32mm, width 0.22mm.Carapace small, subrectangular in lateral view. Both ends of shell equal in height and broadly rounded. Dorsal margin straight, with conspicuous antero dorsal angle and obtuse posterodorsal angle; ventral margin obviously concave in the middle. Both valves equal in size, obscurely overlapping. Anterodorsal and median sulci weakly developed. Surface punctate. Prolimnocythere neimongolensis sp. nov. (P1. Ⅰ, figs. 5—9)Holotype Cat. No. 87003, a right valve.Dimensions Length 0.48mm, height 0.32mm.Carapace small, subrectangular in lateral view. Dorsal margin straight and inclined backward, with pronounced anterodorsal and posterodorsal angles; ventral margin concave in the middle. Anterodorsal sulcus long, extending to mid-height. Surface punctate, with two subcentral nodes.Genus Paralimnocythere gen. nov.Type species Paralimnocythere impolita gen. et sp. nov.Diagnosis Carapace small, thick-shelled, subreniform in lateral view. Dorsal margin straight and inclined backward; ventral margin slightly concave in the middle; anterior and posterior margins rounded. Dorsal sulcus absent. Surface coarsely punctate. Inner lamellae narrow; selvage pronounced; pore-canal zone moderate in width, with few straight pore canals. Hinge of right valve a median groove with plate-like teeth at both ends; top of the teeth separated into three terminals. Hinge of left valve a corresponding median ogival ridge with elongated depressions at each end. Adductor muscle scars counting 4 in a nearly vertical row; mandibular muscle scar unknown.Paralimnocytherd impolita gen. et. sp. nov. ( P1. Ⅰ. figs. 10—14 )Holotype Cat. No. 87008, a right valve.Dimensions Length 0.68mm, height 0.44mm.Carapace small, thick-shelled, subreniform in lateral view. Anterior end higher than posterior one; both ends broadly rounded. Dorsal margin straight and inclined backward, forming on obtuse angle with anterior and posterior margins; ventral margin slightly concave in the middle. Surface coarsely punctate.Paralimnocythere erenhotensis gen. et sp. nov (P1. Ⅰ, figs. 17, 18)Holotype Cat. No. 87013, a complete carapace.Dimensions Length 0.54mm, height 0.38mm, width 0.26mm.Carapace small, subreniform in lateral view. Ends broadly rounded; anterior end higher than posterior one. Dorsal margin straight, with conspicuous anterodorsal and posterodorsal angles; ventral margin concave in the middle. Both valves subequal in size; overlapping obscure. Anterior end compressed and moderately convex in dorsal view. Surface coarsely punctate with tubercles and ornamented with posterodorsal and posteroventral nodes.Paralimnocythere spinisalata gen. et sp. nov. (P1. Ⅰ, figs. 15, 16 )Holotype Cat. No. 87011, left valve. Dimensions Length 0.64mm, height 0.40mm.Carapace small, subreniform in lateral view. Anterior end higher than posterior one; both ends rounded. Dorsal margin elongate and nearly stra