290 PAL&OXTOLOQY OF XEW YORK. 



Orthoceras exile. 



PLATES DtXDC PIG. !; I.WX.IV, FIG. 3: 1 WW. PIGS. 1,2.14,15. 



• 

 OiVtoceras exile. Hall. Descriptions of New Species of Fossils, etc., p. 50. 1861. 



Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 78. pi. 8, tig. 5. 1862. 



" Illustrations of Devonian FomOs: Cephalopoda. Explanation of pi. 39, fiff. 8. 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. constrictum 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 Sch<>- 



