J. Knippers, and T. Speck. volume 82 of Stuttgarter Beiträge zur Naturkunde, Serie C, page 10 - 11. Staatliches Museum für Naturkunde Stuttgart, Stuttgart, (2017)
D. Park, and J. Knippers. Conference proceeding of the 9th Asian Pacific Conference on Shell and Spatial Structures (APCS2009), page 147 – 148. Nagoya Japan, (May 2009)