114 NORTH AMERICAN INDEX FOSSILS. 



nounced dorsal lobe, no annular lobes, and no impressed zone. 

 Siluric-Devonic. 



148. N. eugenium Hall. (Fig. 1348.) Devonic. 



Dextrally coiled shells of about one and one half volutions ; aper- 



^ 



Fig. 1348. Ncedyceras eugenmm. (After Hall.) 



ture contracted, opening directly outward; sutures slightly curved 

 and oblique, with slight lobe on ventral side ; surface smooth. 

 Schoharie of New York and Michigan. 



LVIII. GiGANTOCERAS Hyatt. 



Gyroceracones with stout volutions of compressed elliptical form, 

 with long living chambers. Siphuncle large, nummuloidal, empty, 

 near the center. Sutures with broad ventral saddles, dorsal and 

 lateral lobes. Devonic. 



149. G. inelegans (Meek). (Fig. 1349.) Devonic. 



Large, with whorls rapidly enlarging, in contact. Surface smooth. 

 Columbus limestone of Ohio and Michigan. 



LIX. AcTiNOCERAS Bronn. 



Orthoceracones and cyrtoceracones, generally of depressed ellip- 

 tical section, with large and strongly nummuloidal siphuncles, short, 

 compressed funnels and nearly globular sheaths. Internal deposits 

 leave annulated endosiphuncle with tubuli radiating from the 



