•2 [ s PA L^EONTOLO 6 Y OF NE W YORK. 



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

 Knox, and other points in the Helderberg mountains. 



Orthoceras oppletdm, n. sp. 



(PLATES I.XXXI, FIGS. &-12 ; CXII, FIG. 11. 



Shell robust, straight ; tube gradually enlarging. Transverse section subcircular. 



Cbamber of habitation unknown. Air-chambers regular, having a depth 

 of about six mm. 



Septa, and also some portions of the organic deposit, ornamented by fine, 

 irregular, lamellose strise, which are sometimes concentric about different 

 points on the septa and chamber-walls, generally parallel, and running in 

 the direction of the longitudinal axis of the shell. 



The siphuncle is situated at about one-third the diameter of the tube from 

 the ventral (?) side. Its diameter at the septa is very small. Between the 

 septa the characters have not been observed. 



The organic deposit around the siphuncle is similar to that of 0. luxum, 

 forming a sharply furrowed cylinder between the septa — the furrows in this 

 species being much larger and more irregular than in 0. luxum. The depo- 

 sition is carried to such an extent as almost or entirely to fill the cavity of 

 the chambers, as represented in fig. 12, pi. 81. The separate globular masses 

 of the deposit sometimes have a diameter of six mm. Towards the cham- 

 ber of habitation the deposit is at first a large areola, with a lamellose striate 

 margin, and a fascicle of the striae extending to the margin of the septum. 

 On the septa the deposit is composed of very small globular masses, and in 

 appearance is similar to the same deposit in 0. luxum. 



One individual of this species has a diameter of the tube of about forty mm. 



The appearances of the internal mould are sufficiently marked to readily 

 distinguish the species. The peculiarities of the organic deposit and the 

 ornamentation on the septa are very characteristic. 



This species somewhat resembles 0. luxum in the amount and appearance of 

 the organic deposit. It is, however, much more developed and coarser in its 



