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ACKNOWLEDGMENTS
The present study would not been possible without the help of many colleagues. We are especially grateful to the following persons for granting us access to study specimens and for discussions: A. Borodin, I. Belolubsky, V. Zazhigin (Russia), R. Tedford, L. Marcus, M. Dawson, R. Hoffmann, R. Emry, R. Torrington, and R. Voss (USA), Li Chuankuei, Zheng Shaohua, Wu Wenyu (China); and K. Heissig (Germany).
We are grateful to the anonymous reviewers for valuable comments and to L. Taylor for improving our English.
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