Title: Middle and Upper Ordovician encrinurid trilobites from the Maquoketa Formation (Katian) of Iowa and the Table Cove Formation (Darriwilian) of Newfoundland

Abstract: Trilobites are a diverse group of extinct marine arthropods that had a global distribution throughout the Paleozoic Era (541–252 million years ago). One trilobite family, Encrinuridae Angelin, 1854, is known from the Ordovician through the earliest Devonian (485–410 million years ago). This thesis examines seven species of encrinurid trilobites belonging to the subfamilies Encrinurinae Angelin, 1854, and Cybelinae Holliday, 1942. Two species, Cybeloides iowensis Slocom, 1913, and Encrinuroides pernodosus (Slocom, 1913), are revised based on the type material and new specimens from the Upper Ordovician (Katian) Maquoketa Formation of northeastern Iowa. These revisions are accompanied by a review of the history of study of other trilobites from the Maquoketa Formation and a discussion of encrinurid morphology.

Also included are images and discussion of new material of Cybelurus mirus (Billings, 1865) and the proposal and description of four new species attributable to Atractopyge Hawle and Corda, 1847, Cybelurus Levickij, 1962, and a new cybeline genus. These specimens are from the Middle Ordovician (Darriwilian) Table Cove Formation of the east coast of the Great Northern Peninsula of Newfoundland and are secondarily replaced with silica. Secondary silicification preserves exceptional, three-dimensional detail, which allows for observation of uncommonly preserved features. These specimens challenge traditional views regarding cybeline tail structure.