【摘要】 <正> 一、引言1960年,中国科学院兰州地质研究所的同志,在陕北绥德大理河及宁夏回族自治区灵武县回民巷的上三迭统延长羣中,获得了比较大量的淡水瓣鳃类化石,交与笔者进行研究。随后,笔者1961年参加了兰州地质研究所604队,在陕西旬邑三水河、铜川漆水河、延安延水、绥德大理河及宁夏灵武回民巷等剖面的延长羣中,又采集了一部分瓣鳃类化更多还原

【Abstract】 This paper deals with the non-marine lamellibranch fossils collected during 1960—1962 by the members of the Institute of Geology of Lanzhou,Academia Sinica,from theUpper Triassic Yanchang chun（Yenchang group）.The fossil localities are in Suide,Yanan,Tongchuan,Xunyi,and Lingyou districts of North Shanxi,and in Lingwu districtof Ningxia.The Yanchang chun is well-exposed in the eastern part of Eerduosi（Ordos）plat-form,with its greatest thickness exceeding 1300 metres.It is divided by the members ofthe Ministry of Petroleum Industry into five tzus or formations,which are listed belowin descending order:Super-formation—Yanan tzu——Disconformity——5.The Wayaopu tzu（T₃y⁵）:Greenish and whitish grey fine sandstones intercalated with greenish greyand black shales.4.The fourth tzu（T₃y⁴）:Greenish grey cross-bedded sandstones intercalated with shales.3.The third tzu（T₃y³）:Greenish grey sandstones intercalated with greenish grey sandy shales,mud-stones and shales.2.The second tzu（T₃y²）:Greenish grey sandstones and shales,intercalated with black shales.1.The first tzu（T₃y¹）:Greenish grey or red cross-bedded feldspathic thick-bedded sandstones,interca-lated with dark purple sandy shales.——Conformity——Sub-formation——Zhifang chunThe lamellibranchiate fauna described and illustrated in this paper were collectedfrom the second tzu（T₃y²）up to the Wayaopu tzu（T₃y⁵）of the Yanchang chun,nonehas yet been found in T₃y¹.The fossils comprise 16 species,including six new species andone new variety,which belong to 4 genera,they are as follows:Unio huangbogouensis Hua,sp.nov.,Unio ningxiaensis Hua,sp.nov.,Utschamiellalonga Hua,sp.nov.,Utschamiella elliptica Hua,sp.nov.,Utschamiella cf.elliptica Hua,Utschamiella elliptica var.tongchuanensis Hua,sp.et var.nov.,Utschamiella cf.babika-mensis Ragozin,Utschamiella cf.opinata Ragozin,Utschamiella cf.obrutschevi Ragozin,Utschamiella sp.1,Utschamiella sp.2,Utschamiella?sp.cf.U.tungussica Ragozin,Sibireconcha cf.shensiensis（Chow）,Sibireconcha sp.nov.? cf.S.golovae（Ragozin）,Sibireconcha cf.balbinskiensis（Ragozin）,Tutuella?kui Hua,sp.nov.,Tutuella?nuculi-formis Hua,sp.nov.The above-listed fossils belong decidedly to Angara faunas of Early Mesozoic age,with Utschamiella,Sibireconcha and doubted Tutuella as their distinctive members.The genus Utschamiella has so far been known mainly from the Triassic of the Soviet Union.The species Utschamiella cf.opinata Ragozin,Utschamiella cf.babikamensis Ragozin,Utschamiella cf.obrutschevi Ragozin and Utschamiella?sp.cf.U.tungussica Ragozin canbe compared with the equivalent Russian species.The genus Sibireconcha has been con-sidered as an early Jurassic genus.The two species questionably referred to Tutuella alsohave a rather close relationship with the early Jurassic forms.The latter two genera are,however,less in number in our collections,while the genus Utschamiella appears to be thedominant member.The genus Unio has a world-wide distribution from upper Triassicto Resent and none species of the genus has been found from the earlier sediments.Thespecies Unio huangbogouensis（sp.nov.）agrees in some respects with Unio karrooensisCox from the Upper Triassic of South Africa,whereas Unio ningxiaensis（sp.nov.）re-sembles more or less Unio arizonensis Henderson from the Upper Triassic of NorthAmerica.Taking account of the fact mentioned above,the writer is,therefore,of the opinionthat the fossil assemblage described in this paper is of Upper Triassic rather than earlyJurassic of age.The writer wishes to express her sincere thanks to Pro.C.W.Ku of the Institute ofGeology and Paleontology,Academia Sinica,for his encouragement and instructions.DESCRIPTION OF NEW SPECIESFamily UnionidaeGenus Unio Retzius 1788Unio huangbogouensis Hua sp.nov.（Pl.Ⅰ,figs.1—5）Diagnosis:Shell rather large,transversely rhomboidal in outline.Height-lengthratio being 1:2.Anterior end nearly as high as posterior end.Dorsal margin almostparallel with ventral margin.Convexity moderate,with a rounded but less elevated pos-terior umbonal ridge.Description:Shell rather large,transversely rhomboidal in outline.Height-lengthratio being 1:2.Beaks lain at about the anterior one-fourth to one-third of the shelllength.Anterior-dorsal margin short and arched,bending evenly to the regular roundedanterior margin,which in turn smoothly rounding to the ventral border.Posterior dorsalmargin long and nearly straight,forming a rounded obtuse angle with the posterior bor-der.This border sub-truncated or broadly arched,meeting the ventral margin at a roundedsharp angle.Ventral margin gently curved in the anterior part and straight in the pos-terior part.Dorsal and ventral margin almost parallel.Convexity moderate,the greatestshell convexity being at the lower part of the posterior umbonal region.Post-umbonalridge rounded but less elevated,disappeared at the posterior fourth of the shell length.Umbonal region somewhat broad and flattened,beaks slightly rising above the hinge line.Surface marked with fine concentric lines and irregularly spaced coarse wrinkles.The dentition and ligament are observable in several specimens.In the right valveare a pseudocardinal tooth and two long posterior lamellar teeth.The left valve possessestwo lamellars behind the umbo.The pseudocardinals of this valve are impreserved. Measurements（in mm）:┏━━━━━━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┓┃ ┃ Holotype ┃ Paratype ┃ Paratype ┃┃ Specimen ┃ Cat.No.0082 ┃ Cat.No.0083 ┃ Cat.No.0086 ┃┣━━━━━━━━━━━━━━╋━━━━━━━━━╋━━━━━━━━━╋━━━━━━━━━┫┃ Length ┃ 68 ┃ 79 ┃ 79（±） ┃┃ Height ┃ 32 ┃ 35（±） ┃ 38 ┃┃ Beaks to front ┃ 20 ┃ 20 ┃ 25 ┃┃ Length of the hinge line ┃ 30 ┃ 42 ┃ 40（±） ┃┃ Height/Length ┃ 0.47 ┃ 0.44 ┃ 0.48（±） ┃┃ Thickness（two valves） ┃ 10 ┃ 14 ┃ 16 ┃┃ Thickness/Length ┃ 0.14 ┃ 0.18 ┃ 0.20（±） ┃┗━━━━━━━━━━━━━━┻━━━━━━━━━┻━━━━━━━━━┻━━━━━━━━━┛Comparison:According to the shape and dentition,the species here described un-doubtedly belongs to the genus Unio.Of the American species,only Unio emersoniTroxell（1914,p.461,text-fig.3）resembles the described species in its elongated outline.But the shell of the American species is smaller and the posterior border is gently nar-rower.The new species greatly resembles the paratype of Unio karrooensis Cox（1931,p.630,pl.XL,fig.2）,which was discovered from the Upper Triassic of South Africa,in the shape,the position of umbo,the long and straight posterior-dorsal margin.Butthe thickness-length ratios of them are greatly different,being 0.14—0.20 in the formerand 0.36 in the latter.Therefore,they can be easily distinguished.Horizons and localities:This species occurs in（1）the Wayaopu tzu（T₃y⁵）ofthe Yanchang chun,at Huangbogou,Dalihe,Suide district of Shanxi;（2）the second tzu（T₃y²）of the Yanchang chun,at Zhanjiatan,Yanan district of Shanxi.Unio ningxiaensis Hua sp.nov.（Pl.Ⅰ,fig.6,Pl.Ⅱ,figs.1—3）Diagnosis:Shell medium in size,oblong or rhomboidal in outline,rather inflatedto moderately convex.Anterior end short and rounded,dorsal margin parallel with ven-tral margin,posterior margin somewhat obliquely truncated.Posterior umbonal ridgerather strong.Description:Shell medium in size,thick-shelled,oblong to rhomboidal in outline,rather convex to moderately convex,with the greatest convexity at the central part of theposterior umbonal ridge.Anterior end short and rounded,slightly broadening backward.Beaks lain at about the anterior one-third to one-fourth of the shell length.Dorsal mar-gin nearly parallel with ventral margin.Posterior dorsal margin straight,with a length ofabout one-half the shell length.Posterior border slightly oblique-truncated,meeting theventral margin at a well-defined rounded acute angle.Ventral margin nearly straight.Posterior umbonal ridge well-defined and inflated,extending to the posterior ventral end,probably with a slightly depressed sulcus before it.Umbonal region fairly inflated,beaksslightly prominent.Surface marked by concentric lines.Dentition observable in several internal molds.Right valve having a pseudocardinaland a posterior lamellar teeth,left valve possessing two pseudocardinals and two lamel-lars.Anterior adductor scar rather deep,with a pedal scar above its posterior part.There are some variations in the shell form at this species.The beaks of paratype2 are situated more anteriorly than the holotype and paratype 1.The thickness length ratio of the holotype is much smaller than that of paratype 1.It may be originated fromdeformation.Measurements（in mm）:┏━━━━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┓┃ ┃ Holotype ┃ Paratype ┃ Paratype ┃┃ Specimen ┃ ┃ ┃ ┃┃ ┃ Cat.No.0087 ┃ Cat.No.0088 ┃ Cat.No.0089 ┃┣━━━━━━━━━━━━╋━━━━━━━━━╋━━━━━━━━━╋━━━━━━━━━┫┃ Length ┃ 42 ┃ 47（±） ┃ 46 ┃┃ Height ┃ 22 ┃ 26 ┃ 24 ┃┃ Thickness（two valves） ┃ 10 ┃ 20 ┃ 12.5 ┃┃ Beaks to front ┃ 14 ┃ 15 ┃ 12 ┃┃ Length of hinge line ┃ 22 ┃ 25（±） ┃ 28 ┃┃ Height/Length ┃ 0.52 ┃ 0.55（±） ┃ 0.52 ┃┃ Thickness/Length ┃ 0.24 ┃ 0.43（±） ┃ 0.27 ┃┃ Beaks to front/Length ┃ 0.33 ┃ 0.32（±） ┃ 0.26 ┃┃ ┃ ┃ ┃ ┃┗━━━━━━━━━━━━┻━━━━━━━━━┻━━━━━━━━━┻━━━━━━━━━┛Comparison:Of the described species,paratype 1 approaches very closely to Unioarizonensis Henderson（1934,p.259,pl.36,fig.7a—7b）in the well defined posteriorumbonal ridge.Unio ningxiaensis can,however,be distinguished by its smaller shell,themore or less indistinct sulcus before the umbonal ridge and the greatest thickness更多还原