PALAEONTOLOGY OF NEW YORK. 



One fragment embracing the chamber of habitation nearly entire, and a 

 portion of five of the adjacent air-chambers, has a length of eighty-three 

 mm., with diameters of twenty-six and sixteen mm. at the two extremities 

 respectively. A smaller portion of an individual referred to this species 

 has the test preserved over nearly the entire exterior of the tube. 



From O. rudicula, this species may be distinguished by its excentric siphuncle; 

 and from 0. jaculum by its greater apical angle and more frequent septa. 



Formation and localities. In the limestone of the Upper Helderberg group, 

 Clarence Hollow, Erie county, N. Y., and Dublin, Ohio. 



Orthoceras jaculum, n. sp. 



PLATE XXXV, FIG. 12. 



Oitiux-eras molestum. Hall (in part). Illustrations of Devonian Fossils: Cephalopoda. Explanation of 



pJate 35, tig-. 8. 187G. 



Shell straight, regularly expanding. Transverse section circular. Apical 

 angle 6°. Initial extremity unknown. 



A small portion of the chamber of habitation preserved in the specimen, 

 possesses no unusual characters. Air-chambers regular, having a depth of 

 about five mm. adjacent to the chamber of habitation. 



Septa moderately concave ; concavity equal to an arc of about 85°. 

 Sutures straight and horizontal. Traces of an areola are seen, surrounding 

 the insertion of the siphuncle, with an expansion and vascular markings 

 extending to the ventral margins of the septa. The ventral margins of the 

 septa, and the posterior portion of the cast of the chamber walls, arc 

 elevated into transverse nodes, which become more conspicuous toward 

 the apex of the tube. This elevation is evidently an extension of the areolar 

 deposit around the siphuncle. 



Siphuncle large, moniliform, subcentral, nearer to the ventral side of the 

 tube, expanding in the cavity of the air-chambers to twice its diameter at 

 the septa, which is nearly equal to the depth of the chambers, or more than 

 one-third of the diameter of the tube. 



