206 PALJEOMTOLOGY 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 nun. Surface marked by numerous strong, irregular, longitudinal 

 ridges, with lesser intermediate ridges and fine striae, crossed by sharp, cren- 

 ulating, concentric stria-. 



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 O. 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. — Annulatei forms. 

 Orthoceras crotalum. 



PLATES XLII, FIGS. 1-9, 11, 12; LXXXII, FIGS. 1-6 ; CXIII, FIG. 13. 



Orthocrraa 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 : Cephalopola. 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 



