ABSTRACT Cephalopods of the order Lituitida Starobogatov, 1983 from the late Darriwilian and early Sandbian strata of Estonia are revised herein. During that time, the lituitids reached their peak abundance and were among the key components of cephalopod faunas on Baltica, as well as in other mid- and low-latitude palaeogeographic locations. The Estonian lituitids mostly come from localities representing more off-shore environments with deeper-water sedimentation in the Middle Ordovician. This supports previous assumptions that lituitids preferred pelagic environments and were capable of long-distance migration. In the studied lituitid collection, two genera were identified – Lituites Bertrand, 1763 and Ancistroceras Boll, 1857. Three species – Ancistroceras ristnensis sp. nov., Ancistroceras vahikuelaensis sp. nov. and Lituites nehatuensis sp. nov. – were newly established. However, species determinations were often hindered by high intraspecific variability and fragmentary preservation. Investigation of cameral deposits using median sections showed that: connecting rings in chambers with deposits are commonly broken or missing; oriented fragments of connecting rings are present, sometimes overgrown by primary deposits; several generations of primary deposits can be developed; simultaneous presence of both broken and intact connecting rings in the same specimen is usual. These observations elucidate the formation of cameral deposits in lituitids. Currently, this process is explained either by passive deposition from cameral fluids, or active secretion by cameral mantle. The evidence collected herein from Estonian lituitids reveals, however, that both modes of formation might have occurred successively during the lituitid ontogeny and that a gradual, life-time destruction of connecting rings was possibly involved.

中文翻译：

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来自爱沙尼亚上达里维利安和基底桑比亚（中上奥陶纪）的头足类动物

摘要 1983 年来自爱沙尼亚达里维利安晚期和桑比亚早期地层的 Lituitida Starobogatov 目头足类动物在此进行了修订。在那段时间里，短鳍足类动物的丰度达到了峰值，是波罗的海以及其他中低纬度古地理位置头足类动物群的关键组成部分。爱沙尼亚 lituitids 主要来自代表更多离岸环境的地方，在中奥陶世有更深的水沉积。这支持了先前的假设，即 lituitids 更喜欢远洋环境并且能够进行长距离迁移。在研究的 lituitid 集合中，确定了两个属 - Lituites Bertrand，1763 和 Ancistroceras Boll，1857。三个物种 - Ancistroceras ristnensis sp。十一月，Ancistroceras vahikuelaensis sp. 十一月 和 Lituites nehatuensis sp。十一月 – 新成立的。然而，物种确定往往受到高种内变异性和零碎保存的阻碍。使用中间断面对相机沉积物的调查表明：有沉积物的腔室中的连接环通常会损坏或丢失；存在连接环的定向碎片，有时被原生沉积物覆盖；可开发几代原生矿床；在同一个试样中同时出现断裂和完整的连接环是很常见的。这些观察结果阐明了 lituitids 中照相机沉积物的形成。目前，这个过程可以通过相机液的被动沉积或相机罩的主动分泌来解释。然而，本文从爱沙尼亚 lituitids 收集的证据表明，