CEPHALOPODA. 
249 
aspect in this species. 0. luxum lias not the lamellose-striate markings on the 
septa, and the position of the siphuncle is very different. The septa are also 
more distant in this species. 
This form is comparatively rare; only four imperfect specimens have been 
observed in the large collections made from the different localities. 
Formation and locality. In the Schoharie grit at Schoharie, N. Y. 
Section b.—Slender forms, with numerous regular septa. 
v 
Orthoceras procerus. 
PRATES XXXV, FIGS. 15, 10; LXXVIII A, FIGS. 1-8; RXXIX, FIGS. 5-8. 
Orthoceras procerus, Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 35, fig. 4. 1S76. 
Shell straight, slender, very gradually enlarging from the apex. Transverse 
section subcircular. The apical angle in different individuals measures 6°, 
7^°, and 8°. The initial extremity of the shell is unknown. 
The chamber of habitation is large, measuring from 80 to 100 mm. in 
length. Aperture unknown, but probably entire, with a constriction of the 
tube below. The air-chambers are numerous, having a depth of five to six 
mm. in the larger part of the tube, where the diameter is about 
twenty-five mm.; while in the smaller portion of the tube they are about 
four mm. in depth, the diameter at the same point being seventeen mm.; 
and in both cases the tube is a little compressed. Toward the apex, where 
the tube has a diameter of only eight mm., the air-chambers have a depth of 
four mm., or about the same as in the larger portion of the tube. In 
another specimen not compressed the septa are distant five mm., where the 
diameter of the tube is eighteen mm. In specimen, fig. 8, of pi. 78 A, there 
are twelve chambers in the space of fifty-five mm., the diameters at the two 
extremes being twenty-two and twenty-six mm. respectively. In another 
individual of this species there are nine chambers in fifty-four mm. 
The septa are thin, moderately concave, the depth of the curvature being 
about equal to the distance between the septa, or to an arc of 95° to 98°. 
32 
