CEPHALOPODA. 249 



aspect in this species. 0. luxum has 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. 



Orthoceras procerus. 



PLATES XXXV, PlOfl. 15, 16; LXXVIII A, FIGS. 1-8; LXXIX, FIGS. 5-8. 

 OrtJircerax procerus. Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 35, fig. 4. 1876. 



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 



