Xiphosura, the so-called horseshoe crabs, are a group of extant marine chelicerates that have a fossil record extending back to the Lower Ordovician. Their temporal range, coupled with a supposed record of bradytelic evolution has made them a focus of palaeontological consideration for over two centuries. As such, there are an array of taxa erected during the 20^th century that have remained unexamined in light of new material and revised phylogenetic theories. Stem xiphosurids in particular require further research to uncover the diversity and disparity of non-crown group horseshoe crabs. To align with the recent increase in mid to late Paleozoic horseshoe crab research, we reconsider the stem xiphosurids “Kasibelinurus” randalli and “Bellinurus” alleganyensis from the Late Devonian of Pennsylvania and New York State. We conclude that they are synonyms and belong in neither Kasibelinurus nor Bellinurus, and the new genus, Patesia, is erected to accommodate them. Reconsidering stem xiphosurids highlights that particularly in the Late Devonian there was a high disparity of form. One such stem xiphosurid may represent the morphological stock that gave rise to the Carboniferous taxa and the first xiphosurid radiation.

Xiphosura，即所谓的马蹄蟹，是一组现存的海洋螯蟹，其化石记录可追溯到下奥陶统。它们的时间范围，加上假定的慢进化记录，使它们成为两个多世纪以来古生物学研究的焦点。这样，有分类群20中竖立的阵列^次，在光的新材料和修订系统发育理论仍然未经审查世纪。尤其是茎 xiphosurids 需要进一步研究以揭示非冠群鲎的多样性和差异。为配合最近古生代中后期马蹄蟹研究的增加，我们重新考虑了茎 xiphosurids“ Kasibelinurus ” randalli和“ Bellinurus”” alleganyensis来自宾夕法尼亚州的晚泥盆世和纽约州。我们得出结论，它们是同义词，既不属于Kasibelinurus也不属于Bellinurus，并且新属Patesia的建立是为了容纳它们。重新考虑茎 xiphosurids 突出显示，特别是在晚泥盆世，形态差异很大。一个这样的茎 xiphosurid 可能代表产生石炭纪分类群和第一个 xiphosurid 辐射的形态种群。