No. 4] Proc. Japan Acad., 64, Ser. B (1988) 81 21. Relation between the Silurian Trilobites o f Japan and the Mongolian Geosyncline By Teiichi KoBAYASHI, M. J. A. (Communicated April 12, 1988) In Japan the Silurian trilobites are now counting more than 60 species in 29 genera of seven families in the range from upper Wenlockian to upper Ludlovian which are found in seven areas among which the Yokokurayama formation in Shikoku is richest, yielding about 50 species in 29 genera (Kobayashi, 1988a). The next is the Hitoegane fauna in the Hida plateau containing some ten species in seven or more genera. A few others are known from Hikoroichi, Ofunato, the Kitakami mountains and from Gionyama formation in Central Kyushu (Koba- yashi, 1988b) . This copious fauna is compared here to the neighbouring ones in Eastern Asia. During the Middle Palaeozoic era there was the Koreo-Chinese land covering North China, South Manchuria and Korea on the continental side of Japan, although a small marine invasion has taken place temporarily from the Japan Sea side into the Korean peninsula. Between this land and the Angara land of Central Siberia there was the Mongolian geosyncline in which the thick Palaeo- zoic sediments collectively called the Manmo group were accumulated (Kobayashi, 1971, 1984). In Manchuria Yabe and Eguchi (1944) discovered Silurian corals near Kirin. Later Kuo Hong-tsun (1962) described therefrom the late Wenlock- early Ludlovian trilobites as follows : Encrinurus sinicus Kuo Otarion di ff ractum conveximarginatum Kuo Otarion sphaericum Kuo Calymene cf. blumenbachi Brongniart. Warburgella wudaogouensis Nan, 1980 and Phacops shetaensis Nan, 1980 were added to them from Heilongjiang, where the former is Middle Silurian and the latter Upper Silurian. Prior to this Kazanski (1914) has reported Calymene blumenbachi from the upper Amur valley. Later Tuvanella and others were found in Transbaikalia and the Zeya basin and Scotiella (?) sp. and Eudolatites orientalis Maximova (1969) were described also therefrom. Beyond the Great Khingan Range the Upper Silurian Bateabao fauna of Inner Mongolia comprises 13 species in 10 genera as follows; Scutellum partschi Barrande Scutellum sp. inlet. Ungliproetus unguloides (Barrande) Cyphoproetus sp. inlet. Cheirurus strabo Weber Cheirurus shetaensis Nan Sphaerexochus bate boensis Nan Coronocephalus ulangabensis Nan Coronocephalus sp. inlet. Gravicalymene xibineense Nan 82 T. KOBAYASHI [Vol. 64(B), Homalonotus sp. inlet. Phacops shetaensis Nan Reedops shetaensis Nan. Cheirurus strabo by Nan. (1976) is probably congeneric with Pseudo- cheirurus gomiensis. Cyphoproetus, Sphaerexochus and Phacops occur also in the Yokokurayama limestone. Scutellum partschi referred now to Kosovopeltis which is another genus known from the Yokokurayama limestone. Coronocephalus ulangabensis indicates the northern limit of the generic distribution. Phacops shetaensis is a trilobite known also from the Upper Silurian Duhe stage in Heilongj ian (Nan tai-rong, 1981) and Encrinurus cf. sinensis together with Encrinuroides sp. is reported from the Middle-Upper Silurian Ketotiekedaban group of Western Tienshan. In western Mongolia and Tuva the Silurian rocks are wide spread. Tscherny- sheva (1937) has described the following trilobites: Lichas (Corydocephalus) sivovae Tschernysheva Lichas (Corydocephalu,s) cf. hirsutus Fletcher Homalonotus (Trimerus) mongolensis Tschernysheva Dalmmniturus weberi Tschernysheva. Dalmaniturus is an indigenous genus in the Silurian of Central Asia. As- suming that Dalmmniturus to be a member of the Calmonidae, flourished in the southern continents in the Devonian period (Struve in Treatise, 1959), it may be a link from Ordovician Phacopidae in Europe to the Devonian genera, and Scotiella ( ?) sp. of the Upper Amur is another link. Corydocephalus Hawle and Corda, 1847 is now synonymized with Trochurus Beyrich, 1845. These two trilobites suggest that the trilobite beds of the northwestern slope of the Terekte ridge, Western Mongolia are probably Wenlockian. Encrinuroides meijiangensis Zhang is described from the Silurian Wenquan group of Kuenlun in the upper part of the Xierqianhe (Zhang, 1981). Platy- coryphe sinensis (Lu) and Dalmanitina (Dalmanitina) nachengensis Lu from the Dalmanitina beds at Nanzhen, Shaanxi and Dalmanitina (Dalmanitina) ovata Qu and D. (D.) wuningensis Lin from the Mayingou formation in Gansu mark the lowest horizon of the Silurian Lungmachi series. T ewonia is a new genus founded on Tewonia clava Zhou, nov. from the Lower Silurian Zhouqu group in Gansu. Kosovopeltis guanyuanensis Chang is a Middle Silurian trilobite from Ningjiang, Shaanxi (Zhou et al., 1982). As summarized above, the trilobites have thrived in the Mongolian sea in the Wenlockian-Ludlovian age. Among them, however, the endemism was so strong in the Dalmaniturus fauna that it includes no common genus with the neighbouring faunas. In looking through the other faunas however, their close relationship with the Japanese fauna is undeniable, as pointed out below. 1) The Kirin trilobites of Northeast China consists of four species in three genera, namely Encrinurus, Otarion and Calymene, all of which are found in the Japanese fauna. 2) Encrinurus sinicus of Kirin and also E. cf. sinicus of Tienshan reveal close resemblance with Encrinurus ishii and its allies of Japan. 3) The rich Bateabao fauna represented by 13 species in 10 genera among which more than a half, namely Kosovopeltis, Cyphoproetus, Pseudocheirurus, Spharexochus, Calymene and Phacops are common with the Japanese fauna. No. 4] Silurian Trilobites Japan 83 Table I. Silurian trilobite families and genera in the Mongolian geosyncline 4) Kosovopeltis occurs also in the Middle Silurian of Shaanxi, but the Lower Silurian trilobites of Shaanxi and Gansu are quite distinct from the Japanese fauna. This is because no Lower Silurian trilobite is as yet known from Japan. Thus the trilobites of Japan are closely related to those of the Mongolian geosyncline and particularly so to the Kirin fauna, the status suggesting that the Mongolian geosyncline has been confluent with the Chichibu geosyncline of Japan on the east side of the Korean peninsula in the Silurian period. References Kobayashi, T. (1971) : The Manmo group of the Mongolian geosyncline in Manchuria and adjacent areas. Geology and Mineral Resources of the Far East, vol. 3, pp. 3-69. (1984) : The history of the eastern wing of the Mongolian geosyncline. Proc. Japan Acad., 6OB, 103-105. 84 T. KOBAYASHI [Vol. 64(B), Kobayashi, T. (1988a) : The Silurian cephalopods and trilobites from the Yokokura- yama Formation, Shikoku, Japan. Pron. Japan Acad., 64B, 1-4. (1988b) : The Silurian trilobitess in. Japan, ibid., 64B, 5-8. Kuo Hong-tsun (1962) : Some Silurian trilobites from Er-tao-gou group of Jilin. Acta Pal. S inica, 10(3), 377-381, 2 pls. Lu Yen-Hao et al. (1974) : Chinese Trilobites. 2 vols., 766 pp., 135 pls. Nan Run-shen (1976) : Trilobita, pp. 333-352. Palaeontological Atlas of North China. Fasc. Inner Mongolia (1), Palaeozoic Geol. Surv. Inner Mongolia Autonomic Prov. and Geol. Inst. North China (co-ed.). (1980) : Trilobita, pp. 484-519. Palaeontological Atlas of North East China (1), Palaeozoic Fasc. Chen-yang Geol. Survey. Yabe, H., and Eguchi, M. (1944) : Discovery of Pseudomphyma in the limestone of Erh- tao-kou near Kiturin, Mansyu. Proc. Imp. Acad., 20, 382-385. Zhang Tai-rong (1981) : Trilobita, pp. 134-213. Palaeontological Atlas of Northwest China (2). Xingiang Weiwuer Autonomic Prov. Late Proterozoic-early Palaeozoic. Geol. Surv. Party of Xinjian Geol. Bureau, Xinian Geol. Surv. Petroleum. Zhou Zhi-j ang, Li Jin-Song, and Qu Xin-gou (1982) : Trilobita, pp. 215-294. Palae- ontological Atlas of Northwest China. Xijiang Weiwuer Autonomic Province. Fasc. 1..