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; LXXYI, FIG. 1; LXXVII, FIGS. 1-8; LXXVIII, FIGS. 5-7; LXXVIII B, FIG. 3; 
LXXXI, FIG. 13; CXII, FIGS. 12-U. 
Orthoceras luxum , 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 11°. 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 fiat, 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 
is 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 
