530 



MOLLUSCA 



PHYLUM VI 



Family 10. Trochonematidae Zittel. 



Shell pyramidal, turbinate or discoidal, dextral or sinistral, with internal nacreous 

 layer. JVIiorls convex, with one or more longitudinal keels, and slightly iindulating 

 transverse striae or ribs. Aperture rounded, sometimes ivith faint notch. Operculum 

 unknown, presumably horny. Marine. Cambrian to Cretaceous. 



This extinct group is very abundant in the Paleozoic, and notably so in Jurassic 

 rocks. The shells, as a rule, are highly ornamented, and have been associated by some 

 with the Littorinidae, by others with the Turbinidae or Purpurinidae. They form 

 a distinct family, wliich is best placed in the neighbourhood of the Turbinidae and 

 Trochidae. 



Trochonema Salter. Pyramidal to turbinate, deeply umbilicate, longitudinally 

 keeled and transversely striated. Aperture round ; the umbilicus surrounded by a 

 keel. Cambrian to Silurian. 



Eunema Salter (Fig. 876). Pyramidal, with acute, elongate spire, and no umbilicus. 

 Whorls with two or more spiral keels, and strong transverse striae. Aperture oval, 

 slightly notched anteriorly. Ordovician to Devonian. 



Fig. 870. 



Eunema strigilata Sal- 

 ter. Ordovician ; Pau- 

 quette Falls, Canada. 



Fio. 877. 



Cyclone.ma bilix Conrad. 

 Ordovician ; Cincinnati, 

 Ohio. 



Fig. 878. 



Amherleya capitanea 

 Miinst. Upper Lia.s ; La 

 Verpilliere, near Lyons, 

 France. 



Cyclonema Hall (Fig. 877). Turbinate, whorls inflated and ornamented with fine 

 spiral striae ; apertui-e rounded, peristome discontinuous. Ordovician to Devonian. 



Strophostylus and Holupea Hall ; Gyronema Ulrich. Ordovician and Silurian. 

 Dyeria Ulrich. Ordovician. Biicanospira, Ulrich. Silurian. 



Amberleyn Morr. and Lye. (Eucyclus Deslongch.) (Fig. 878). Turbinate to 



Fig. 879. 



Pfntyar/ra impressa 

 (S('hafhautl). Lower 

 Lias ; Hoclifellen, 

 Bavaria. 



Fic. SSO. 

 Cirrus nodosiis Sowh. Lower Oolite ; Yeovil, England. 



pyramidal, with deep sutures, and no umlnlicus. Sjiiral keels usually nodose or sjjiny, 



