140 



Cincinnati Society of Natural History. 



little less than the length of three air chambers in any part 

 of our specimens, except, of course, adjoining the body cham- 

 ber, where, as in all species of Orthoceras, the air chambers 

 are not completely developed in length. However, the second 

 air chamber from the body chamber, in our specimen, has 

 attained nearly its entire length, and from appearances the 

 third chamber was fully developed. The siphuncle is eccen- 

 tric and much expanded within the air chambers. It would 

 be regarded as a rather large and strongly beaded siphuncle. 

 The septa are thin and on the surface transverse, and every 

 thing indicates a thin external shell. The surface markings 

 and initial extremity are unknown. 



This species is distinguished by its great size, great length, 

 large body chamber, distant and highly convex septa, and 

 large, beaded siphuncle. It has, apparently, no near affinity 

 with any described species from rocks of the same age. When 

 compared with Orthoceras amplicameratum, from the Trenton 

 Group, of New York, the shell is larger, more rapidly taper- 

 ing, septa more distant, and siphuncle more strongly beaded, 

 It would throw no light on it to compare it with Orthoceras 

 medullar e y from the Niagara Group, of Illinois, for the surface 

 of that species is marked with strong, sharp, subequal longi- 

 tudinal striae, which are cancellated by fine transverse striae, 

 which our species could not have possessed. 



This species occurs in the lower part. of the Hudson River 

 Group, at and about Cincinnati. It has been found in the 

 banks of the Ohio opposite Cincinnati, in Ludlow, and at the 

 lower part of Covington, Ky. The specimens illustrated and 

 described belong to the collections of the authors. 



Orthoceras aebersi S. A. Miller. 



Plate S, Fig. 1 , lateral view, showing part of the shell with its 

 longitudinal furrows; Fig. 2, part of another specimen with 

 the outer shell removed; Fig. 3, a single chamber, showing 

 the convexity of the septa; Fig. 4, an end viezv, showing the 



. eccentric position of the siphuncle. 



Shell straight, rather below medium size, and gradually and 

 rapidly enlarging from the apex to the body chamber. The 



