中文摘要：

渭河地区位于我国中部,包括甘肃、宁夏及陕西部分地区,新生代化石资料丰富.口盖作为我国陆相地层中广泛分布且类型丰富的化石,目前多报道于20世纪七、八十年代,主要见于奥陶纪、白垩纪-古近纪地层,且主要分布于我国东南部地区,西部仅在西藏有所见及.随着近些年渭河地区工作的不断进展,在渭南沈河张家坡剖面发现大量口盖化石,主要产于上新统游河组下部地层,岩性以灰绿色、青灰色砂质泥岩及砂岩为主.由于岩性疏松、成岩作用弱,通过清水浸泡、80目筛子淘洗、筛选及稀盐酸处理,对比早期研究成果,根据其形态结构特征,鉴定出4属12种（Mirolaminatus,Assiminea,Parafossarulus和Pseudemmericia）,其中包括8个新种,均为上新世地层中首次发现的腹足类口盖化石.简单归纳了口盖化石演化序列,指出腹足类口盖化石的大小及厚度不能作为口盖化石演化特征,且钙化的比角质的更进步.该化石的发现为腹足类动物群、上新统口盖化石研究及古环境恢复提供了新的证据.

英文摘要：

The Weihe area, containing plenty of Cenozoic fossils, is located in the middle of China, extending parts of Gansu, Ningxia and Shaanxi provinces.The Gastropod opercula are widely distributed fossils in China with various types deposited in continental strata.It was revealed by previous studies mostly in 1970~80s that fossil opercula are rich in strata of Ordovician, Cretaceous and Paleogene.Opercula were widely found throughout Southeast China, while in the west of China, opercula were only discovered in Tibet.There, however, were few related reports since 1980s.With in-depth study in the Weihe area in recent years, we discovered a large number of Gastropod opercula from the Zhangjiapo Section（34°25＇46＂N, 109°31＇35＂E） in the Weihe area.Fossils mainly exist in the bottom of Pliocene Youhe Formation, which mainly consists of greyish-green and steel-gray sandy mudstone and sandstone.From the section, about 3kg rock samples were collected.These rocks are unconsolidated with weak diagenesis.After being soaked in water for several days, these samples were elutriated and screened with 80 mesh sieve, and then treated with diluted hydrochloric acid.As a result, a total of 187 pieces of fossils were yielded.In comparison with previous discovered species, and based on their structure characteristics, 4 families and 12 species were identified, including 8 new and 4 old species.These fossils are 8 pieces of Mirolaminatus, 73 pieces of Assiminea, 65 pieces of Parafossarulus, and 41 pieces of Pseudemmericia. These fossil Gastropod opercula were found for the first time from Pliocene strata in the Weihe area.According to our study, together with previous studies, we summarized the evolution sequence of opercula and revealed that thickness and size of Gastropod opercula cannot be regarded as one of the evolution characteristics, and that calcified individuals were more advanced than cutinized ones.The discovery of opercula in the Weihe area provides new evidence for studies of Gastropod fauna, Pliocene opercula and