CEPHALOPODS. 227 



Orthoceras arcuoliratum HALL. 

 Orthoceras arcuoliratum Hall, 1847: Pal. New York, vol. I, p. 198. 



A rather small species, cylindrical, with slightly raised 

 undulatory ridges running obliquely around the shell, and 

 finely lined in a longitudinal direction. 



Horizon and localities. Silurian, Trenton limestone : 

 Louisiana. 



Orthoceras jolietense MEEK & WORTHEN. 



Orthoceras jolietense Meek & Worthen, 1865 : Proc. Acad. Nat. Sci., Phila., 



p. 256. 

 Orthoceras jolietense Meek & Worthen, 1875: Geol. Sur. Illinois, vol. VI, 



p. 465, pi. xxvi, fig. 5. 



Shell large, very long and slender, tapering rapidly, and 

 with the septae very distant. Cross-section elliptic. 



Horizon and localities. Silurian, Niagara limestone : Graf- 

 ton ( Illinois ). 



Orthoceras medullare HALL. 

 Orthoceras medullare Hall, 1860: Geol. Sur. Wisconsin, Kept. Progress, 



p. 4. 



Orthoceras stricelineatum McChesney, 1861: New Pal. Foss., p. 94. 

 Orthoceras medullare Hall, 1867: New York State Cab. Nat. Hist., 20th 



Reg. Rep., p. 412, pi. xx, figs. 1-2. 

 Orthoceras medullare Meek & Worthen, 1875 : Geol. Sur. Illinois, vol. VI, 



p. 504, pi. xxvi, fig. 1. 



Shell large, tapering gradually. Surface marked by prom- 

 inent longitudinal ribs, crossed at regular intervals by trans- 

 verse carinse, giving a beautifully cancellated effect. 



Horizon and localities. Silurian, Niagara dolomite: 

 Grafton ( Illinois ). 



Spurious and Doubtful Species. 



Goniatites holmesi Swallow, 1860 : Trans. St. Louis Acad. Sci., vol. I, p. 

 659 . Kinderhook limestone : Cooper county. Cannot be recog- 

 nized. 



Goniatites morganensis Swallow, 1860 : Trans. St. Louis Acad. Sci., vol. 

 I, p. 659. Kinderhook. Not recognizable. 



Nautilus (Cryptoceras) capax Meek & Worthen, 1865 : Proc. Acad. Nat. Sci., 

 Phila., p. 262. Coal Measures : Charboniere. Name preocpupied. 



Nautilus gilpini Swallow, 1860 : Trans. St. Louis Acad. Sci., vol.1, 

 p. 658. Coal Measures : Wayne county. Too imperfect for recog- 

 nition . 



