CEPHALOPODA. 275 



and a diameter at the aperture of ninety-five mm. A septate fragment 

 containing thirteen air-chambers has a length of 155 mm. 



This species differs from O. Bebryx in its larger size, more distant septa, and 

 cylindrical siphuncle. It more nearly resembles 0. Pelops and 0. Zeus of the 

 Schoharie grit, but it has not the constriction of the chamber of habitation of 

 the latter, and the prominent areola around the siphuncle of the former species. 



Formation and localities. In the Hamilton group on Lake Erie shore, and at 

 Otisco, Onondaga county, N. Y. 



Orthoceras Bebryx. 



PLATE* XXXVIII. FIG 10; XXXIX, FIG. Ij I.XXXIH, FIG. 14; LXXXIV, FIG& 11, 12. 



OiHniceras Bebryx, Hail. Illustrations of Devonian Fossils: Cephalopoda. Explanation of plate 39, 



fig?. 1, 2. 187«. 



Shell robust, straight, regularly enlarging from the apex. Transverse section, 

 allowing for the degree of compression, subcircular. Apical angle eight to 

 ten degrees; the variation being due to the compressed condition of the 

 specimens. 



Chamber of habitation not fully observed. Air-chambers regular, increas- 

 ing in depth from the apex, and varying in different individuals from six to 

 ten mm. 



Septa smooth and thin, so far as observed. Sutures, in specimens not 

 distorted by compression, straight and horizontal. 



Siphuncle monilifonn, expanding between the septa, and having a diameter 

 equal to, or two-thirds, the depth of the air-ehambers. The septa are usually 

 macerated, or broken from compression, and the position of the siphuncle 

 has not been satisfactorily determined. One small fragment, referred to 

 this species with doubt,. re tains the septa, and shows the siphon in a slightly 

 excentric position. 



The test has not been preserved. The casts of the interior indicate a 

 trans versly lamellose-striate surface. 



A fragment, embracing a portion of the chamber of habitation and seven- 

 teen of the adjacent air-chambers, has a length of 220 mm. 



