29G 
PALAEONTOLOGY OF NEW YORK. 
Siphuncle subcentral. In its passage through the air-chambers the ele¬ 
ments have not been observed. 
Test thin, rarely preserved. Tube ornamented by regular, low undula¬ 
tions, which are often elevated into distinct annulations toward the apex; 
becoming obsolescent on the outer part of the chambered portion of the tube, 
and often not at all perceptible over the chamber of habitation. The annu¬ 
lations have a distance of about eight mm. where the tube has a diameter 
of thirty mm. Surface marked by numerous strong, irregular, longitudinal 
ridges, with lesser intermediate ridges and fine striae, crossed by sharp, cren- 
ulating, concentric striae. 
The internal mould usually preserves the longitudinal ridges, and some¬ 
times the impressions of the concentric striae; but these markings are much 
more subdued than on the exterior of the test. 
A fragment, showing ten annulations, has a length of fifty-eight mm., with 
diameters of twenty-one and twelve mm. respectively, at the two extremities. 
A larger portion of another individual has a diameter of thirty-eight mm. 
This species is distinguished by the annulations and undulations of the tube 
and the surface-markings, in which it differs from 0. CEdipus and 0. profundum, 
of the Upper Helderberg group, and from 0. Creon, of the Schoharie grit. 
Formation and localities. In the Hamilton group, at Geneseo, Livingston 
county; Pratt’s Falls, Onondaga county; and in the calcareous beds of the 
group in Madison county, N. Y. 
Section d.—Annulated forms. 
Orthoceras crotalum. 
PRATES XLII, FIGS. 1-9, 11, 12; LXXXII, FIGS. 1-6; CXIII, FIG. 13. 
Orthoceras crotalum, Hall. Descriptions of New Species of Fossils, etc., p. 50. 1861. 
“ “ “ Fifteenth Rep. State Cab. Nat. Hist., p. 78. 1862. 
“ “ “ Illustrations of Devonian Fossils: Cephalopoda. Explanation of pi. 42. 1876. 
Shell straight, regularly and rapidly enlarging from the apex, and becoming 
cylindrical toward the aperture. Transverse section subcircular. Apical 
angle about 9°. Initial extremity obtuse, having a diameter of about 1.5 
