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Panderian Organs of trilobites, some pits, grooves, furrows, projection and pygidium, are coaptative structure about enrollment on the doublure of trilobites.
The author expounded the structure of shield of stopping enrollment from the following three aspects:
1. Cephalic doublure and the marginal region of dorsal cephalic;
2. Coaptative structure on the pleural;
3. Coaptative structure of the pygidium doublure and dorsal pygidium.
The compositive of coaptative structure in enrollment of trilolbites could subdivided roughly into seven categories:
1. Sphaeroidal enrollment;
2. Hemspiral enrollment;
3. Unrolled spiral enrollment;
4. Spiral enrollment;
5. Unroll-inverted spiral enrollment;
6. Inverted spiral enrollment;
7. Discoidal enrollment.
Hemisoiral enrollment equal to“unrolled spiral enrollment" from Borgstrom(1973). These categories of trilobites enrollment depend on defferent coaptative structure and Panderian organs. In the Ordovician, second is Hemispiral enrollment, most of trilobites are sphaeroidal enrollment
In this paper. The author studied and counted 102 species of enrollment specimens of the Ordovician trilobites from China and some parts of the world in the following ways.
1. From enrollment types: Spaeroidal enrollment (58%)；Hemispiral enrollment(14%)；Discoidal enrollment (8%）；Spiral enrollment have not been found.
2. From stage（six stages) in the Ordovician: Llanvernian (the first peak) enrollment specimens (25%)；Ashgilian(the
second peak）enrollment specimens（22%）；Other four stages(53%)．
3. From relation of habits and enrollment: nekton enrollment (40%)；Pelgic enrollment (31%)；Nekton-benthic enrollment (21%)；drill-mud enrollment (8%).
Studying trilobites enrollment is helpful to research ecology.

CONTENTS
1. Preface
2. The carapace of Ordovician trilobites and Panderian Organ on the doublure
3. The enrollment of Ordovician trilobites
4. The example and discussion of Panderian organ and enrollment of Ordovician Trilobites
5. Table Statistics of Panderian Organ and Enrollment of Ordovician Trilobites
6. Reference
7. Abstract
8. Plates and explanation

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