PLATE XXXIX 



PAGE 



Figs. 1, 2. ORTHOCERAS SUBULATUM Hall (?) 308 



1. Partly exfoliated living chamber. 



2. Septum of the same, showing position of siphuncle. 



Romney formation, Hamilton member, right bank of Potomac, 

 3 miles below Cumberland. 



Figs. 3, 4. ORTHOCERAS SUBULATUM Hall 308 



3. The apical portion of a specimen, showing the regular increase in 



the depth of the air-chambers from the apex to the larger ex- 

 tremity. 



4. A septum, showing the position of the siphuncle. 



Hamilton formation, New York. 



Figs. 5-8. ORTHOCERAS CONSTRICTUM Vanuxem 309 



5. Partly exfoliated living chamber. Romney formation, Hamilton 



member, Oldtown Road near Cumberland. 



6. A fragment retaining a portion of the living chamber and twenty- 



one air-chambers. 



7. A fragment of the living chamber, with two of the attached air- 



chambers. 



8. A septum, showing position of siphuncle. 



Hamilton formation, New York. 



Fig. 9. ORTHOCERAS CF. EXILE Hall 310 



Specimen showing seven air-chambers. Romney formation, Hamilton 

 member, Evitts Creek. 



Figs. 10, 11. ORTHOCERAS EXILE Hall 310 



10. Living chamber with two air-chambers. 



11. Septum of same, showing the circular, transverse section of the 



tube and the excentric position of the siphuncle. 

 Hamilton formation, New York. 



122 



