266 
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 0. 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, PIG. 12. 
Orthoceras molestum, Hall (in part). Illustrations of Devonian Fossils: Cephalopoda. Explanation of 
plate 35, tig - . 8. 1870. 
Shell straight, regularty 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, are 
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. 
