564 MOLLUSCA SUB-KINGDOM VI 
Family 5. Popanoceratidae. Shells similar to Arcestidae (except in primitive 
Popanoceras, which is discoidal and compressed). Saddles have entire monophyllic 
bases, and dorsal sutures are similar to those of Prolecanitidae in some genera; but in 

Popanoceras multistriatum, Gemm. Fic. 1163. 
Permo - Carboniferous ; Sosio, Sicily. _ Cyelolobus Stachei, Gemm. Permo-Carboniferous ; Sosio 
2/5 (after Gemmellaro). Sicily (after Gemmellaro). 
others they become more complex and show approximation to Arcestidae. Antisiphonal 
lobe trifid, but otherwise entire in primitive forms, becoming complex in specialised 



















3. 1164. 
Arcestes intuslabiatus, Mojs. Upper Trias ; Steinbergkogel, near Hallstadt, Austria. A, B, External aspect. 
C, Median section. D, Suture-line. 
genera, Aperture with hyponomic sinus in primitive genera, but acquires faint crests 
in shells that resemble Arcestidae. 
Stacheoceras, Waagenoceras, Hyattoceras, Gemm.; Popanoceras, Hyatt (Fig. 1162) ; 
Parapopanoceras, Haug ; Cyclolobus, Waagen (Fig. 1163). Permian and Trias. 
Family 6. Arcestidae. Mojsisovics (pars). Smooth, globose, deeply involute 
