642 



MOLLUSCA 



PHYLUM VI 



Fio. 1219. 



Septa of Shximardites simondH 

 Smith. Coal Measures ; Texas 



Subfamily B. Cyclolobinae Zittel. 



Forms as a rule much larger and with more complex septa than in the Popano- 



ceratinae. There is a distinct tendency towards a 

 phylloid development of the saddles. This subfamily 

 probably came from the Popanoceratinae, although the 

 most primitive and oldest genus assigned to the group, 

 Shumardites, almost certainly is descended directly from 



Schistoceras. 



Shumardites Smith (Fig. 1219). Carboniferous. Cyclo- 

 lolus Waagen (Fig. 1220); JVaagenoceras Gemm. (Fig. 

 1221). Permian. 



Sulifamily C. Arcestinae 

 Mojsisovics. 



This comprises smooth, globose, 

 deeply involute anarcestean forms, 

 discoidal only in primitive genera. 

 Gerontic living chamber usually more 

 or less contracted laterally, becoming 

 sometimes subacute at the venter ; in 

 extreme age depressed, and truncated 

 or concave at the aperture. The 

 latter has typically in the ephebic 

 stage a low In-oad ventral crest, but 

 loses this in the parage ron tic sub- 

 stage, and acquires a ventral sinus 

 simulating that of Paleozoic and more 

 primitive forms. Saddles and lobes 

 completely divided by more or less 

 complex marginals, the monophyllic 

 outline being completely obscured 

 except in the young, and in dorsal 

 sutures of some species. Siphonal 

 saddles long, and not very deeply 

 incised by marginal lobes. Antisi- 

 phonal lobe bifid or trifid, and com- 

 plex in specialised forms. Other 

 dorsals may also become quite com- 

 23lex, and as a rule are completely 

 divided, although of course simpler 

 than the external sutures. Dorsal 



sutures in the young resemble those of the Popanoceratinae. Funnels prosiphonate 



in ephebic stage. 



Sphingitea, Arcestes (Figs. 1139, 1222), Stenarcestes, Proarcestes, Pat-arcestes, 



Ptycharcestes, Joannites (Fig. 1223), Didymites Mojs. (Fig. 1224). Trias. 



Fig. 1220. 



Cyclolohus stacTiei Gemm. Permo-Carboniferons ; 

 Sosio, Sicily (after Gemmellaro). 



Fin. 1221. 



Septa of Waagenoceras hilH Smith. Permian 

 Texas, x 1/2 (after J. P. Smith). 



Family 14. Cladiscitidae Mojsisovics. 



Involute, laterally compressed, ivith abruptly rounded ventral shoulders and flattened 

 venter. Umbilicus closed. No contraction of the ajjerture, and no labial constrictions. 

 Body-chamber long. Surface spirally striated. Lobes and saddles numerous, deeply and 



