270 /'.tLJEO.\TOLOGV OF NEW YORK. 



Orthoceras viator, n. sp. 



PLATE XXXVII, FIG. S. 



Orthoceras baculum. Hall (in part). Illustrations of Devonian Fossils: Cephalopoda. Kxplanation of 



plate 37, fig-. 2. 1876. 



Shell straight, very gradually enlarging to the aperture. Transverse section 

 circular. Apical angle 2^°. Initial point unknown. 



Chamber of habitation cylindrical, well developed, length five times the 

 diameter at the last septum. The tube regularly and very gradually expands 

 to a point near the middle, from which it gently contracts for a distance 

 equal to one-fourth the entire length of the chamber; then expanding 

 rapidly, and again constricting, it enlarges somewhat abruptly to the aper- 

 ture. Air-chambers regular, so far as observed, having a depth of about 

 four mm. 



Septa and siphuncle not observed. 



The test, as preserved on some portions of the tube, has had a thickness 

 of 1.5 mm., and the exterior was marked by fine lamellose lines of growth. 



The appearances of the internal mould with the double constriction of the 

 outer chamber are very characteristic. 



A specimen, consisting of the chamber of habitation nearly entire, and 

 two of the air-chambers, has a length of 104 mm., with a diameter of twenty- 

 four and twenty-two mm., respectively, at the two extremities. 



This species is distinguished from 0. stylus, of the Schoharie grit, by its 

 larger size and the constricted chamber of habitation. It more nearly resem- 

 bles 0. exile, of the Hamilton group, but differs in its somewhat larger size, 

 more cylindrical form of the tube, and much larger chamber of habitation. 

 0. Telamon has comparatively deeper air-chambers, and has not shown evidences 

 of a constricted chamber of habitation. 



Formation and locality. From the Upper Helderberg limestone at Clarence 

 Hollow, Erie county, N. Y. 



