CEPHALOPODA— ORTHOCHOANITES. 



65 



Plectoceratida. 

 XVIL Aphetoceras Hyatt. 

 Gyroceracones, sometimes with last whorl deviating from the 

 spiral, not in contact at any stage, compressed elliptical, or oviform 

 in section; the venter narrower than the dorsum; siphuncle sub- 

 ventran; surface smooth. Ordovicic. 

 58. A. farnsworthi (BilUngs). (Fig. 1273.) Ordovicic. 



Fig. 1272. Spyroceras nuntium. Fig. 1273. Aphetoceras farnsworthi^ X 



part of internal mold, X %> and en- y^. (After Billings, Pal. Foss. ) 

 largement of surface. (After Whit- 

 field.) 



Septa crowded ; siphuncle propioventran ; last whorl strongly 

 deviating. 



Beekmantownian of Lake Champlain region. 

 59. A. americanum Hyatt. Ordovicic. 



Whorls becoming laterally compressed in adult; coil regular; 

 last whorl deviating but slightly; abdomen more or less flattened 

 in last stages ; sutures with ventral and dorsal saddles. 



Beekmantownian of Newfoundland. 



XVni. Barrandeoceras Hyatt. 

 Whorls barely in contact, or with very slight contact furrow; 

 venter usually narrower than dorsum; siphuncle near but above 

 5 



