描述Plagiolaria nandanensis Chang的头、胸肋和尾的腹边缘,指出它的颊角腹边缘与Phacops guang-xiensis Chang近似,头前腹边缘宽,并靠后。胸肋腹边缘保存较好,肋腹边缘上的潘杰尔脊形态变化不大,但前后则有微小差异。尾腹边缘分两部分,在近外侧有一较明显的凹槽,这是当三叶虫卷曲时与头腹边缘结合的相适应的构造。没有发现卷曲标本,在南丹,90%以上几乎全是蜕壳标本,头与胸尾部分离。但是从腹边缘构造看,比Plagiolaria具更完善的卷曲能力,像其他的phacopids一样,头与尾的结合相当完善,胸肋末端在卷曲时插入头颊角腹边缘的锯齿形沟中,各肋端以其腹边缘上的潘杰尔脊挡住后一肋端的前缘。

Many calcareous phacopid specimens have been reported from the U.S and Europe. In China phacopid specimens representing the genera Phacops and Plagiolaria have been reported from Lower and Middle Devonian Mudstones in the Nandan district, Guangxi.The name Plagiolaria was introduced by Kegel (1952) as a new name for Plagiops Kegel, 1932, based on Phacops plagiophthalmus Reinh. Richter 1865. Species of the genus have been reported from Germany, Viet-Nam, Thailand and China. The species studied here is Plagiolaria nandanensis from the lower Middle Devonian Tangding Formation in the Luofu district, Nandan County, Guangxi Province. Specimens are usually preserved in mudstone; some specimens are silicified. The trilobite species is associated with tentaculites and brachiopods. Previous descriptions largely based on internal moulds are therefore inexact as far as the exterior morphology is concerned. In 1987, Han Nairen, Zhou Youmin and Wang Jialing collected many specimens of P. nandanensis in order to study the moulting. Among the specimens were two silicified thoracopygidia. In 1989, Professor Li Youxing provided the authors with a perfect silicified ventral specimen of P. nandanensis Chang in which the doublure of the thorax is well exposed (Pl.1, fig.3). In this specimen, the doublure of the first nine pleural ends is preserved. In 1987, Han and others collected several specimens exposing thoracic doublure.

Q915.819.1