244 PALEONTOLOGY OF NEW YORK. 



distribution, so far as known, this species is confined to the upper beds of the 

 Schoharie grit. 



Formation and locality. Schoharie grit, Schoharie, N. Y. 



Orthoceras luxum. 



plates xxxv, figs. 4-7; lxxvi, fig. i ; i.xxvii, figs. 1-8; lxxviii, figs. 5-7; lxxviii b, fig 8; 



lxxx1, fig. 18 ; cxii, figs. 12-14. 



Orthoceras luxwn. Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 35, fig. 5. 1876. 



Shell straight, regularly and gradually enlarging from the apex. Transverse 

 section, in the better preserved individuals, circular. Apical angle varying, 

 owing to the compressed condition of the specimens, from 9° to 1 1°. Apex 

 unknown. 



The chamber of habitation is rarely preserved, and has no unusual char- 

 acters. So far as observed, it regularly enlarges to the aperture without any 

 constriction or contraction. Aperture unknown. The air-chambers are 

 regular, gradually increasing in depth from the apex to the grand chamber. 

 The depth of the interseptal spaces varies from six to three mm. in the same 

 and in different individuals. In specimens retaining their normal form, the 

 outer walls are flat, not deviating from the general attenuation of the tube. 

 In compressed forms, the walls are conspicuously concave. 



Septa thin, regularly concave ; the concavity equal to an arc of about 

 113°. Many of the specimens vary from this amount of concavity according 

 to the various degrees of compression and distortion to which they have 

 been subjected. The convex side of the septum is marked by a. distinct 

 areola surrounding the siphuncle. and extending in a kind of vascular expan- 

 sion unequally, and on one side, often reaching to the margins of the sep- 

 tum, and affecting the ventral portion of the cavity. This areolar marking 

 U often thickened, becoming striated at the margin, and spreading over the 

 septum as a mammillary organic deposit. 



Siphuncle central, moniliform, greatest diameter between the septa equal 

 to nearly three times the diameter in its passage through the septa, or equal 



