2S0 PALEONTOLOGY OF NEW YORK 



individuals, and over different portions of the tube. There are also slight 

 variations in the depth of the chambers. It is distinguished from 0. aptum, 

 with which it is associated, by its more distant septa, its greater apical angle, 

 and straight, septal sutures. And from O.fustis by the greater development of 

 the chamber of habitation, the absence of any decided constriction or abrupt 

 contraction at the aperture, the depth of the chambers, the excentric and 

 smaller siphuncle, and the surface ornamentation. In many respects It resem- 

 bles 0. luxum; but the position of the siphuncle, its elements, and the dimen- 

 sions of the tube, are very different. From the other species in the present 

 group, it is distinguished by its proportions, surface characters and the organic 

 deposit. 



In this species, as in all the species described in this volume, which have 

 developed an organic deposit, the appearances of this deposit depend upon the 

 mode of weathering, the conditions of preservation, the material filling the 

 cavities, and the manner in which the chambers separate at the septa. The 

 elevated areola and its processes may separate from the convex surface of the 

 septa, and remain imbedded in the filling of the air-chambers, leaving the septa 

 apparently smooth. Or it may remain attached to the convex surface, giving 

 to the septa a totally different aspect. From the condition of preservation in 

 many of the specimens, the raised areola, which has been considered as a 

 deposit, may be explained by supposing the deposition to have been made on 

 the concave surface of the septa, from the margins toward the siphuncle ; and 

 which has remained attached to the filling of the air-chambers, leaving an 

 elevated expansion around the insertion of the siphuncle on the convex .side of 

 the septa. In support of this view, the areola is always larger and has less of 

 an elevation near the chamber of habitation, gradually diminishing in diameter, 

 and becoming more prominent toward the apex, where the amount of organic 

 deposition is at the maximum. AVhatever may have been the original purpose 

 of the deposit, the shells in which it is more fully developed always present 

 the appearance of deterioration or disease. 



The markings on the ventral walls of the air-chambers, as described, are 

 evidently the cast or the reverse of the original conditions. These suggestions 



