636 



MOLLUSCA 



PHYLUM VI 



groups under the Pinacoceratidae may have no near kinship with each otlicr but 

 may rather be merely i^hylogerontic developments in different stocks. 

 j__ Pinacoceras Mop. (Figs. 1194, 1195); Placites Mojs. 



AdL EL 



Pinacocerm metttrnicM (Hauer). Keuper ; Someiiiukogel, near Hallstadt, Austria, 

 Suture-line reduced (after Hauer). 



Family 9. Glyphioceratidae Hyatt. 



Form, robust and involute, or evolute and trapezoidal in section. Body -chamber long. 

 Labial constrictions always present. Spiral ridges often present, especially on the venter. 

 External septa somewhat like those of the Primordialinae, but the dorsal or internal septa 

 have narrovi saddles and an interior lateral lohe on either side of the pointed anti- 

 siphonal lobe. 



Siphuncle small, and funnels generally prosiphonate. Aperture usually with 

 hyponomic sinus, but some species have ventral crests during ephebic stages. Shells 

 smooth, tuberculated or costated, but costae do not cross the venter as a rule. Venter 

 .sometimes with well-marked longitudinal ridges. 



This group is probaldy descended from the Cheiloceratidae, and is the ancestral 



stock of the Tropitidae and the Arcestidae, 

 possibly also of the Ptychitidae. Muenstero- 

 ceras, Gastrioceras (Figs. 1196, 1197), Glyphio- 



¥ia. lino. 



Gastrioceras josaae (M. V. K.). Permo- 

 Carboniferous ; Artinsk, Ural. 



Gastrioceraii diadciiia (Goldf.). 

 Lower Carboniferous Lime- 

 stone ; Choquier, near Liege, 

 Belfriura. 



Fl(3. 1199. 



GU/phioccras sphaericum Faralcgoceras newsoini 



(Goldf.). Lower Carboniferous Smith. Coal Measures ; 



Limestone ; Suttrop, West- Arkansas, x V2 (after J. P. 



phalia. Smith). 



ceras (Fig. 1198), Paralegoceras (Fig. 1199), Schistoceras Hyatt; Pericyclus Mojs. ; 

 Pronannites Haug. ; Praeghjphioceras Wedekind. Devonian and Carboniferous. 



Family 10. Thalassoceratidae Hyatt. 

 Forms robust, involute, laterally compressed. Septa from goniatitic to ceratitic to 



