636 



MOLLUSCA 



PHYLUM VI 



gi-oups imder tlie Pinacoceratidae may have no near kinship with each other but 

 niay ratlier be inofely phylogerontic developments in different Stocks. 

 Pinacoceras Mois. (Figs. 1194, 1195); Placites Mojs. 



AtlL EL 



Pinacoceras metternichi (Hauer). Keuper ; Someraukogel, near Hallstadt, Austria. 

 Suture-line reduced (after Hauer). 



Family 9. Glyphioceratidae Hyatt. 



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

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

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

 have narrow saddles and an interior lateral lobe on either side of the pointed anti- 

 siphonal lobe. 



Siphuncle sniall, and funnels generally prosiplionate. Aperture iisually with 

 hyponomic siniis, but some species liave ventral crests diiring ephebic stages. Shells 

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

 sonietimes with well-niarked longitudinal ridges. 



This group is proba})ly 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- 



Fiti. 1196. 



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

 Carboniferous ; Artinsk, Ural. 



Fig. 1197. 



Ga'itrioceras (Ziade?>ui(Qoldf.). 

 Lower Carbon iferous Lime- 

 stone ; Choquier, near Liege, 

 Belgium. 



Fig. 1198. 



GlypMoccras sphaericum 



(Qoldf.). Lower Carboniferous 

 Liniestone ; Suttrop, West- 

 phalia. 



Fig. 1199. 



Paralegoceras newsovii 

 Smith. Goal Measures ; 



Arkansas. 

 Smith). 



X 1/2 (after J. P. 



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

 Pronanmtes Hang. ; Praeglyphioceras Wedekind. Devonian and Carboniferous. 



Family 10. Thalassoceratidae Hyatt. 

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



