290 



Founded upon a compressed fragment "from the shales of 

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



Obthoceras nuntium. Hall. 

 (Fig. 225. ) (Pal. N. Y., Vol. V., Ft. 

 II., p. 299, Pis. XLIII., LXXXII.) 



Distinguishing ( 'haracters. — 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 : 

 numerous regular horizontal annu- 

 lations; regular longitudinal stria*, 

 and concentric lines of growth. 



Found 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 Averv's Creek 

 (very rare). 



Orthoceras ema- 



CERATUM. Hall. 



(Fig. 225 A.) (Pal. 

 N. Y., Vol. V.. Pt. II., p. 292, PL XXXIX. ) 



Distinguishing ( haracters. — Sub-circular 

 transverse section; apical angle four and fio. 225c Ortho- 



, , . . . . , , ceras constrictum. 



one-nnn degrees; regular air cnam bers, grad- Living chamber, 



. . showing constriction, 



uallv increasingin depth towards the living and several air cham- 



1 ^ bers (after Hall). 



chamber: straight and horizontal sutures. 



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

 Erie. (Hall.) 



Fio. 225 B. rthoce ra s sp 



Eighteen ^lilc Creek (after Hall). 



