Nearly continuous carbonate deposition more than 70 million years ago on the Panthalassan buildup is recorded in the Upper Paleozoic limestone blocks and breccias in the Itsukaichi–Ome area, west Tokyo. These blocks and breccias resulted from the collapse of the seamount and tectonic mixing with trench-fill deposits and are contained in the Jurassic accretionary complexes of the Chichibu Terrane. One hundred and five species of Permian foraminifers from 64 localities are distinguished in them, in addition to the previously reported 65 species of Carboniferous ones from 36 localities. These faunas are identical with or comparable to those known from 24 fusulinacean zones among 26 that are distinguished in the Japanese Upper Paleozoic. Neoschwagerinids, and some of schwagerinids and verbeekinids, are very characteristic in the Chichibu faunas of the Panthalassan Province. These Middle Permian fusulinaceans are more closely related faunistically to those of some exotic terranes in the circum-Pacific than of the coeval Akiyoshi faunas and the Kurosegawa faunas of Japan. In relation to the provincialism and endemism of fusulinaceans, and paleo-position and travel history of circum-Pacific terranes, important fusulinaceans in this area are represented by: 1) Acervoschwagerina, a specialized, large-sized, inflated schwagerinid in the Artinskian (Yakhtashian); 2) Parafusulina japonica, a schwagerinid entirely lacking in the Permian terranes of Japan in the upper Wordian (upper Murgabian); 3) many diversified Misellina in the Kungurian (Bolorian) and lower Roadian (lower Kubergandian); and 4) well-traceable Maklaya–Neoschwagerina–Yabeina evolutionary lineage in the upper Roadian to Capitanian (Midian).