CEPHALOPODA. 293 



Orthoceras aulax, n. sp. 



PLATE LXXXIV, FIG. IS. 



This species is indicated from a fragment of the chamber of habitation and 

 several of the attached air-chambers, which retains characteristic and distinc- 

 tive surface-markings. The tube is slender, and the enlargement very 

 gradual. Air-chambers, septa and siphuncle unknown. Surface marked by 

 regular, numerous, low, rounded transverse ridges, about twelve in the space 

 of ten mm. The interspaces, or furrows, are regularly concave, and have a 

 width equal to the ridges. Portions of the surface also show that it was 

 traversed by fine, sharp, longitudinal striae, crossing the ridges. Length of the 

 fragment, eighty mm. 



The specimen is from the soft shales, and is much compressed. It occurs 

 with O. emaceratum, from which it is distinguished by its surface ornamentation. 



Formation and locality. From the shales of the Hamilton group at Hamburg, 

 Erie county, N. Y. 



Orthoceras scintilla, n. sp. 



PI.ATKS I. XXXIV, FIGS. 19-21; CXIII, FIGS. 6-12. 



Shell minute, slender, regularly .and gradually enlarging from the apex. 

 Transverse section circular. Apical angle about 3°. Initial extremity 

 unknown. 



Chamber of habitation not observed. Air-chambers increasing in depth 

 from the apex toward the outer chamber; having, at that point, a depth 

 equal to the diameter of the tube, or from one to two mm. 



Septa thin, moderately concave, smooth, with the exception of a large cir- 

 cular areola around the insertion of the siphuncle. Sutures straight and 

 horizontal. The areola is always well defined, constituting tbe base of the 

 cone .around the siphuncle in the anterior portion of each air-chamber. 



Siphuncle large, central, cylindrical, indenting the septa, having a diameter 

 of about one-third the diameter of the tube. Toward the outer chamber 



