294 



volution; narrow and profound umbilicus ; large ventricose 

 living chamber ; very concave septa; large, abruptly expand- 

 ing siphuncle; concentric and radiating lines, and obscure 

 low rounded nodes. 



Found only in the Nautilus bed, near the base of the 

 Hamilton group, in Avery's Creek, and in Erie Clin'. 



Nautilus (Centroceras*) marcellensis. (Yanuxem.) 

 (Fig. 228.) (Pal. N, Y., Vol. V., Pt. II., p. 428, Pis. LXV., 

 CIX.) 

 Distinguishing Characters.— Discoid, somewhat com- 

 pressed . form; 

 contiguous, but 

 not embracing, 

 volutions: wide 

 and deep umbili- 

 cus, exposing en- 

 tire lateral faces 

 of the inner volu- 

 tions; angularity 



of 



m argi ns 



of 



Fig. 228. Nautilus marcellensis. A young specimen on 

 stone natural size (original) ; adult (after Hall) reduced to VOllltlOllS glVUlg 

 one-fourth natural size. 



a sub-quadrangu- 

 lar cross-section ; septal sutures forming a distinct angular 

 saddle on the umbilical margin, a broad shallow lobe on 

 the lateral face of the volution, a distinct angular saddle 

 on the outer margin, and a rounded lobe on the outer face 

 of the volution; siphuncle near the outer margin of the 

 volutions. 



Found in the impure limestone band, which forms the 

 dividing line bet ween the upper Marcellus and the Transition 

 shales in Erie Cliff. 



Note — This species has heretofore been recorded only from 

 the Goniatite limestone, which forms the dividing line 



♦Centroceras, Hyatt, "includes Devonian species, with much compressed whorls, 

 abdomen often hollow, sometimes narrow, with one row of tubercles along the edge of the 

 abdomen on either side; the sutures have deep V-shaped ventral lobes, deep lateral and 

 dorsal lobes ; no annular lobes in species observed. The dorsum is frequently gibbous, and 

 has an impressed zone only in the more compressed and more involute species/ Type, 

 C. Marcellense. (Gen. Foss. Ceph., p. 283.) 



