642 



MOLLUSCA 



PHYLUM VI 



Subfamily B. Cyclolobinae Zittel. 



Forms as a rule mucli larger and witli 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 groiip, 

 Shumardites, almost certainly is descended directly from 

 Schistoceras. 



Shwnardites Smith (Fig. 1219). Carboniferous. Gyclo- 

 lohus Waagen (Fig. 1220); Waagenoceras Gemm. (Fig. 

 1221). Permian. 



Fio. 1219. 



Septa of Shumardites simon(lM 

 Smith. Goal Measures ; Texas. 



Subfamily 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 broad ventral crest, but 

 loses this in the paragerontic 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- 

 plex, and as a rule are completely 

 divided, although of course simpler 

 , . ^, than the external sutures. Dorsal 



in epheWc sta e^''''''^ '''''^^^' ^^""'^ °^ ^^' Popanoceratinae. Funnels prosiphonate 



Sphingites Arcestes JFigs. 1139, 1222), Stenarcestes, Proarcestes, Pa.'arcestes, 

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



Fig. 1220. 



Cyclolöbus stachei Gemm. Permo-Carboniferous ; 

 Sosio, Sicily (after Gemmellaro). 



Fig. 1221. 



Septa of Waagenoceras Ulli Smith. Permian • 

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



Family 14. Cladiscitidae Mojsisovics. 



..Jr Tli '^1 '7^7f ^' ^^'^^ '^^^^Vtly rounded ventral Shoulders and flattened 



nndTrJ,n^fr' T V ^' '^^''^^^^^on of the aperture, and no labial constrictions. 

 Bodychamher long. Surface sp^rally striated. Lobes and saddles numerous, deeply and 



