252 PALEONTOLOGY OF NEW YORK. 



show an organic deposit. It is closely allied to 0. collatum, and may be 

 distinguished by its more distant septa and their greater concavity. The speci- 

 mens do not preserve enough of the chamber of habitation to admit of 

 comparisons with 0. collatum in this particular. 



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

 Helderberg range. 



Orthoceras collatum, n. sp. 



PLATE LXXX, FIGS. 1, 8, 4. 



Shell straight, regularly and gradually enlarging from the apex to a point near 

 the aperture. Transverse section subcircular, often much flattened from 

 compression. Apical angle varying from 4° to 6° in the specimens. Initial 

 point unknown. 



Chamber of habitation large, slightly expanding beyond the general 

 enlargement of the tube, to a point anterior to the middle, where it is 

 abruptly constricted. In front of the constriction the tube expands gradu- 

 ally towards the aperture. Aperture not observed. Air-chambers regular, 

 having a depth of about eleven mm. ; walls flat and smooth. The ventral 

 side is indicated by a low, longitudinal carina on the chamber walls, which 

 is more prominent on the anterior portion. This line is shown on the casts 

 of the interior, and has a width of about one mm. 



Siphuncle large, slightly excentric, having a diameter at the septa of 

 nearly four mm. Its elements in its passage through the chambers have 

 not been observed. 



The characters of the test and its ornamentation are not shown on any of 

 the specimens at hand. It was probably thin and has been dissolved, leav- 

 ing a cast of the interior. 



The internal mould is essentially smooth. The ventral carina and the 

 marked constriction of the chamber of habitation are the only distinctive 

 features. 



