Calymenesun granulosa Lu的背壳及接合构造

EXOSKELETON AND COAPTATIVE STRUCTURE OF CALYMENESUN GRANULOSA LU

描述了Calymenesun granulosa Lu的腹边缘及结合构造,并讨论了此种三叶虫的卷曲机制.认为当其卷曲完善时,尾"边缘"及部分胸肋纳入头颊下,以往描述为尾边缘的部分实际上是尾背结合沟所在位置.卷曲形式为半螺旋卷曲.

Calymenesun is widely distributed in the Upper Ordovician strata of South China, and has only been discovered in China up to now. A study on the internal and external casts of many Calymenesun granulosa specimens preserved in siliceous concretions has revealed some new exoskeletal structures. A long and uptilted cephalic spine is clearly shown on the cephalic internal cast. The palpebral lobe is vertical and erpendicular to the cephalic level. The rostral plate is fan-shaped, forming an edge in the front, but is arcuate in the posterior margin. During enrollment of the trilobites, a vincular furrow appears in the dorsal part of the pygidium, and the outer pleural part bears a few posterior pleurae. The terminal axial segment extends downwards beneath cephalon and rostral plate, thus forming the 'hemirolled spiral enrollment'. Except a few parts, the outer pleurae overlap each other by degrees posteriorly. The location of the vincular furrow moves gradually close to the base of the outer pleurae in a backward direction.