41-j PALEONTOLOGY OF NEW YORK. 



aperture; but there are indications in the stride of an obscure sinus on each 

 side, half way from the centre to the lateral margins on the ventral fac of 



the shell. 



The specimen described has a length of about seventy nun., and includes 

 era! imperfectly preserved air-chambers. Of this length, fifty-five mm. 

 pertain to the grand chamber, which is equal to the greatest transverse 

 diameter. The dorso-ventral diameter of twenty-eight mm. is somewhat 

 reduced from the natural proportions by pressure ; while the transverse 

 diameter is slightly increased from the same cause. 



With only a single imperfect specimen, the determination is quite unsatis- 

 factory ; but this form possesses so many characters in common with A T . liratus 

 that its specific relations may be inferred, the features being those which 

 might be presented in the immature condition of that species. 



Formation and locality. In the arenaceous beds of the Hamilton group, in 

 Madison county, N. Y. 



Nautilus bucinum. 



PLATES LX, FIGS. 1-4; CVI, FIGS. 4-7; CVII, FIGS. 2-5; CLX, FIGS. 1, 2. 



Nautilus bwiiiiiin, Ham,. Illustrations of Devonian Fossils : Cephalopoda, pi. 60, figs. 1-4. 1876. 

 . Compare Gyroceras expanxum, Sakma.nx. Danker and von Meyer's Palxoutographiua. 1853. 

 Mot Nmvtihu fxpantum, Sowbebt. Min. Conchol., vol. 5, p. s:!, tab. 458, fig. 1. 1825. 

 tiijroceras txpanxum, vnr., Hall. Thirteenth Rep. N. Y. Stale Cab. Nat. Hist., p. 104. 1860. 



Siikll subovoid, ventricose, rapidly expanding toward the aperture. 



Volutions about one and a half or two, contiguous, not embracing, 

 exposed for their entire length. Umbilicus large, profound. Transverse 

 section broadly elliptical. The dorso-ventral and transverse diameters about 

 as three to four, three to five, and five to seven, measured on different parts 

 of the chambered portion of the shell, some variation being due to pressure. 

 The enlargement of the volutions is very rapid, the transverse diameter 

 increasing to nearly double in less than a single volution preceding the 

 grand chamber. 



Chamber of habitation large, rapidly expanding from its base, and becom- 

 ing very ventricose. Longer than wide. Its capacity about twice as great 



