290 



Founded upon a compressed fragment "from the shales of 

 the Hamilton gTOup, at Hamburg, Erie County, N. Y." (Hall. ) 



Orthocekas xuntu'm. Hall. 

 (Fig. 225.) (Pal. N. Y., Vol. Y., Pt. 

 n., p. 299, Pis. XLHl., LXXXII.) 



Distinguishinf>- ( linrn cters. — Regu- 

 larly and rapidly enlarging tube; 

 sub-circular transverse section; api- 

 cal angle about nine degrees ; nu- 

 merous regular air chambers, 2 mm. 

 deep, where diameter is 10 mm. ; 

 septal concavity greater than depth 

 of chambers; sub-central siphuncle: 

 numei'ous regular horizontal annu- 

 lations; regular longitudinal stria^ 

 and concentric lines of growth. 



I^ound in the Tri- 

 lobite beds, at Sec- 

 tion 8, on the 

 Lake Shore, and in 

 Avery's Creek; also 

 in the shales, two 

 to four feet below 

 the Trilobite beds, 

 in Avery's Creek 

 (very rare). 



Orthoceras ema- 



CERATUM. Hall. 

 Eighteen Mile Creek (after Hall)." ( JTJfy 2254. ) (Pal 



N. Y., Vol. v., Pt. n., p. 292, PL XXXIX.) 



Distinguishing ( liaracters.— Sub-circular 

 transverse section; apical angle four and 

 one-half degrees ; regular air chambers, grad- 



FlG 



Orthoceras 



Fig. 225C Ortho- 

 c e r (I .s coHstrictum. 

 Living chamber, 

 showing constriction, 



uallv increasing in depth towards the living and several air cham- 



r^ I '^ bers (after Hall). 



chamber; straight and horizontal sutures. 



Found in the Hamilton shales, on the south Shore of Lake 

 Erie. (Hall.) 



