250 PALEONTOLOGY OF NEW YORK. 



Siphuncle small, slightly excentric. Its character in its passage between 

 the septa has not been observed. 



The organic deposit consists of an areola on the septa, surrounding the 

 siphon, from which in some specimens there are obscure, radiating, vascular 

 ridges. On the exterior walls of the air-chambers in the cast, and indicat- 

 ing the ventral side, there is a longitudinal raised line or keel, represented 

 in fig. 4, pi. 78 A. The other specimens also show this line, but it is not 

 represented in the figures. Sometimes the line is made more prominent 

 by a distinct, shallow groove on either side. 



The test is usually so far dissolved, or otherwise removed, that no evi- 

 dence as to its thickness remains. Several of the specimens preserve traces 

 of the surface-markings, which consist of fine and closely arranged sharp, 

 transverse striae, crossed by very fine, longitudinal striae. The transverse 

 stria) curve backward over the dorsal and ventral sides, and forward over 

 the lateral portions of the shell. 



No entire individuals of the species have been observed. One specimen 

 has a length of 260 mm. Others measure about 250 mm. in length, and are 

 incomplete towards the apex, and we may infer that they have been at least 

 100 mm. longer. The greatest diameter in incomplete specimens is less 

 than forty mm. 



This species bears some resemblance to special conditions of O. luxum, but 

 may be distinguished by the excentric siphuncle, and absence of the conspicuous 

 organic deposit. O. inoptatum, pi. 37, fig. 1, is of similar form and proportions, 

 but differs in having a very excentric siphuncle, and no evidences of an areola 

 on the septa. 



This species is unknown to me in any formation except the Schoharie grit. 



Formation and localities. In the Schoharie grit at Schoharie, and in the 

 Helderberg mountains; but is unknown beyond the limits of this formation in 

 the eastern part of the State of New York. 



