The Euloma changshanense Lu, which is collected from the Lower Ordovician in Jiangshan，Zhejiang, is a part of old shield of exuviations. It is an imprint of librigenal doublure. We analyze its process of exuviations through observing the deuterogenous remnants shield and consider that two librigenal cheeks link up in the middle of foreside of cephala. During the exuviations，the body of the trilobite climbed up，separated itself from the foreside of cephala， but the librigenal cheeks were still on the new shield. Then，they were propped up by the new trilobite，the imprint of librigenal doublure in the foreside of cephala was preserved only. It reflects that there was a period of break when the trilobites were exuviating. During the exuviations，there was a time out. Furthermore the new trilobites usually carried or hauled the librigenal cheeks and hypostoma on the old cephala，which made the old shield leave behind the carapace. The status of exuviations happened instantly，and it belonged to autochthonous remains，indicating that trilobite was in the status of sedentary water with abundant sediment supplying. The sediments would bury the trilobite during the exuviations or exuviations shortly. The Yinzhufu Formation at Jiangshan is fairly thick. It is overlain by the Azygograptus suecicus Zone which is at the lower part of the Dawanian stage. In contrast，at Yushan (in Jiangxi Province)，not far away from Jiangshan, the Yinzhufu Formation is overlain by the Tetragraptus approximates Zone which is at the lower part of the Yushanian stage. This indicates that the Yinzhufu Formation is diachronous. However the Euloma changshanensis Lu is always found at the uppermost part of the Yinzhufu Formation on both places， indicating that these trilobites belong to the Lower Ordovician，but they thrived over a long period of time from the late-Tremadoc to the end of Yushanion Stage. It also indicates that the Yinzhufu Formation is relatively thick，but the sedimentary environment did not change much and，even the genus and species such as trilobites，Euloma changshanense and so on changed little. Such a formation is a good stratigraphical interral to study the exuviations of trilobite and the evolutionary progress of the ecological replacement.