2ss 



living chamber twice as long as its median diameter; nu- 

 merous regular air chambers; thin, smooth septa, concavity 

 equal to an arc of 116 degrees: large straight central cylin- 

 drical siphuncle; concentric and longitud- 

 inal stria 1 . 



Found "in the Hamilton group, on Lake 

 Erie Shore * V (Hall, type. ) 



Orthoceras bubulatum. Hall. ( Fig. 

 221.) (Pal. X. Y., Vol. V, Pt. II.. p. 283, 

 Pis. XXXYIIL, LXXXIV., LXXXYI.) 



Distinguishing Characters. — Straight, 

 regularly expanding subulate form : circular 

 cross -section : sub -cen- 

 tral siphuncle: living 

 chamber three times as 

 long as its basal diame- 

 ter: thin, smooth septa, 

 with concavity equal to 

 an arc of about 125 de- 

 grees. 



Found in the upper 

 Moscow shale, two feet 

 from the top, at Section 

 2 (rare) ; in the Encri- 

 nal limestone, at Sec- 

 tion 5 (rare): three feet 

 below the Encrinal lime- 

 stone, at Section G 

 (rare) : and in the Stro- 

 phalosia bed, in Avery's 

 Creek (common ). 



Orthoceras exile. Hall. (Fig. 222.) 

 (Pal. \. V.. Vol. V.. Pt. II., p. 290, Pis. 

 XXXIX.. LXXXIV.. LXXXV.) 



Distinguishing < 'haracters.— St raight, slender, regularly 

 enlarging form, with circular cross-section, and apical angle 

 of five degrees; concavity of septa equal to depth of 



<&m 





mm* 



W 



Fig. 233. Orthoce- 

 ras tela man. The 

 living chamber, with 

 one air chamber at- 

 tached, and basal 

 view of same, show- 

 ing position of si- 

 phuncle (after Hallj. 



Fig. 224. Orthoceras au- 

 lax. A fragmentary speci- 

 men, from Hamburg on- 

 the- Lake (after Hall). 



