CEPHALOPODA. 29 



Orthoceras expositum. 



PLATE CXV1II, FIG. 2. 

 Orthoceras expositum. Hall. Fifth Ann. Rr-pt. State Geologist Expl. pi. (118) 2, fig. 2. 1886. 



Shell large, straight, gradually enlarging to the aperture ; transverse section 

 sub-circular. Apical angle five degrees. Initial extremity unknown. 



Chamber of habitation long, regularly expanding to the aperture, length 

 more than twice the diameter of the tube at the last septum. Air-chambers 

 7 mm. in depth where the tube has a diameter of 37 mm., becoming regu- 

 larly shallower toward the apex of the tube. 



Septa thin, concavity deeper than the depth of the air-chambers. The 

 apical portion of the shell is partially filled with an irregularly vesiculose 

 organic deposit. 



Siphuncle moniliform. excentric. 



Test not preserved. The impression of the shell in the rock shows that 

 the surface was marked by lamellose concentric lines of growth. 



The specimen illustrated has a length of about 300 mm., of which 125 

 mm. belong to the chamber of habitation. 



Numerous fragments of this species are preserved in an iron-ore bed, from 

 Bradford county, Pa. The specimens consist of internal moulds in a ferruginous 

 sandstone, or of calcareous shells imbedded in the sandstone. 



Distribution. In an iron-ore bed of the Chemung group. Canton, Bradford 

 county, Pa. 



Orthoceras consortale. 



PLATE CXV1II, FIGS. 3-5. 

 Orthoceras consortale, Hall. Fifth Ann. Rept. State Geologist. Expl. pi. (US) 2, tigs. 3-5. 1SSG. 



Shell straight, rapidly expanding from the apex to near the aperture ; trans- 

 verse section broadly oval. Apical angle ten degrees. Initial extremity 

 unknown. 



Chamber of habitation not fully shown in the specimens observed, appar- 

 ently short and constricted near the aperture. Air-chambers 5 mm. in 



