242 
PALAEONTOLOGY OF NEW YORK. 
habitation, varying from five to eight mm. This species also presents, in a 
less marked degree, the zoned appearance of 0. cingulum, caused by the 
removal of the shelly margins of the extended septa; otherwise the cast of 
the interior is smooth. 
Septa having a concavity equal to an arc of about 110°. Plane of the 
septa straight, and slightly oblique; convex surface ornamented by an 
elevated areola around the siphuncular scar, and generally by an irregular, 
vesiculose, organic deposit around the siphuncle, which sometimes reaches a 
diameter of more than one-third that of the tube. Occasionally this deposit 
consists of irregular tubercles and flattened expansions, extending nearly to 
the septal margins. The character and appearance of this organic deposit 
on the septa and siphuncle'varies greatly in the same individual, depending 
upon the distance from the chamber of habitation. Near the apex it assumes 
a more marked complexity of detail, often nearly filling the chambers, and 
obscuring the characters of the septa and siphuncle. 
Siphuncle apparently straight, with the walls sometimes variously thick¬ 
ened on the exterior. 
Test unknown. Casts of the interior marked by an elevated line along 
the septate portion, indicating the ventral side of the shell, and free from 
any other markings so far as observed. 
This fossil is only known in a fragmentary condition. When entire, the 
tube probably had a length of one foot and a half, or about 450 mm. 
From 0. Ohioense this species is distinguished by the absence of any curva¬ 
ture of the tube, and by the organic deposit on the septa and siphuncle. It 
resembles 0. ~Pclops in the character of the surface of the casts; but the 
septa are more closely arranged, and their concavity not so great. In the 
incomplete examinations made previously to the publication of the Illustrations 
of Devonian Fossils, this form had not been separated from 0. Pelops, and in the 
crushed and imperfect condition of a large proportion of the specimens of this 
formation, the distinction between the two species is not always conspicuous. 
In the distance of the septa and comparative attenuation of the tube, this form 
differs little from well-preserved specimens of 0. luxum; but the concavity of 
