290 
PALEONTOLOGY OF NEW YORK. 
Orthoceras exile. 
PLATES XXXIX, FIG. 3 ; LXXXIV, FIG. 3; LXXXV, FIGS. 1, 2, 14, 15. 
Orthoceras exile, Hall. Descriptions of New Species of Fossils, etc., p. 50. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 78, pi. 8, fig. 5. 1862. 
“ “ “ Illustrations of Devonian Fossils : Cephalopoda. Explanation of pi. 39, tig. 3. 1876. 
Shell straight, slender, regularly and gradually enlarging from the apex. 
Transverse section circular. Apical angle 5°. Initial extremity unknown. 
Chamber of habitation cylindrical, large; length equal to more than three 
times the diameter at the last septum. Some of the specimens show a broad, 
undefined constriction toward the aperture; but this feature is not always 
conspicuous. Air-chambers numerous, increasing in depth toward the outer 
chamber, varying from two or three mm. to five mm. in the length of 100 
mm., or about thirty chambers. 
Septa smooth, thin, with a concavity equal to an arc of 104°, or equal to 
the depth of the chambers. Sutures straight and horizontal. 
Siphuncle excentric, distant from the nearest point on the walls of the 
air-chambers about one-third the diameter of the tube. Its elements in the 
interseptal spaces have not been observed. The diameter at the septa is 
two mm., where the tube has a diameter of seventeen mm. 
Test and surface-markings not observed. 
Internal mould smooth, showing no traces of the surface-markings, or of 
an organic deposit. 
An individual, retaining the chamber of habitation and about forty air- 
chambers, has a length of 165 mm., with a diameter of fifteen mm. near the 
aperture. Other fragments have been observed belonging to larger indi¬ 
viduals, having a diameter of twenty-three mm. 
This species differs from O. constriction and O. subulatum in its excentric 
siphuncle and more distant septa. The septa are comparatively more frequent 
than in O. Telamon and O. emaceratum, and the siphuncle is smaller and less 
excentric than in the former. It somewhat resembles O. stylus of the Scho- 
