CEPHALOPODA. 
233 
ORTHOCERATA OF THE SCHOHARIE GRIT. 
DESCRIPTIONS OF SPECIES. 
Section a.—Robust forms , showing a gradation from a simple areola on the septum surrounding 
the siphuncle, to a decided and complex organic deposit. 
Orthoceras Pelops. 
PLATES XXXV, FIGS. 1-3; XXXV A, FIGS. 1-6; XXXVII, FIGS. 3,4; LXXVIII B, FIG. 2. 
Orthoceras Pelops, Hall. Descriptions of New Species of Fossils, etc., p. 45. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 73. 1862. 
“ “ “ in part. Illustrations of Devonian Fossils: Cephalopoda, pi. 35. 1876. 
Shell robust, straight, elongate. Transverse section circular in specimens not 
compressed; the flattening often amounts to a change in the relations of the 
diameters of from 1-1 to 1-3. Cone gradually and regularly enlarging 
from the apex. Apical angle 7° to 9^°. Initial extremity unknown. 
Chamber of habitation well developed, sometimes measuring more than 
twenty-five centimetres in length, and at least five or six times as long as 
the diameter at the last septum; a broad,~gentle constriction near the aper¬ 
ture is generally present. Depth of the air-chambers about one-sixth of the 
width of the tube; four to eight in the space of sixty mm., depending on 
the diameter of the tube or the distance from the apex. 
Septa thin, with a small areola around the insertion of the siphuncle, regu¬ 
larly concave; concavity equal to an arc of from 120° to 126^°; part of this 
variation being probably due to compression, or other influences which have 
affected the true curvature. In the more perfect specimens, the sutures are 
horizontal and straight, the various degrees of distortion observed having in 
many cases made them curved and oblique to the axis. 
Siphuncle central, or very slightly excentric; walls thin, seldom pre¬ 
served ; width equal to about two-thirds the depth of the adjacent chambers, 
or approximately from four to five mm. The presence of an areola on the 
septa indicates that the siphuncle was moniliform, or slightly expanding. 
30 
