CEP HA LOPODA. 413 



as all the chambered portion of the shell. Gently constricted near the 

 aperture. Aperture straight, entire, opening horizontally and transverse to 

 the axis of the shell. Margin slightly curving toward the apex on both the 

 dorsal and ventrolateral sides. Air-chambers regular, gradually increasing 

 in depth toward the grand chamber. In a fragment of the chambered por- 

 tion of the tube, measuring about sixty mm. on the curve of the convex side, 

 and having a width of thirty-six mm. in the middle of its length, there are 

 nine air-chambers. 



Septa thin, regular, having a concavity of about 110°, and equaling the 

 depth of one and a half air-chambers ; closely arranged on the axial margin, 

 and distant six to ten mm. on the ventral side. Sutures distinctly marked, 

 and often deeply impressed from the solution or weathering of the septal 

 margins. 



Siphuncle near the concave dorsal side, and about one-fourth or one-third 

 of the dorso-ventral diameter from the surface. Its elements between the 

 septa not observed. 



Test thin, having a thickness of about one mm. on the dorsal side, 

 and from .5 to .75 mm. on the convex ventral side. Surface marked by 

 very fine lines of growth, and by regular, more distant, transverse striae. 

 These are crossed by regular, sharply elevated, revolving striae, of which 

 there are about four in the space often mm. near the aperture, and between 

 these there are finer, irregular striae. The stronger revolving striae are not 

 unfrequentlv very prominent, and assume the character of gentle carina- 

 tiona on the concave side; but they are more subdued upon the convex 

 side. In examples where the shell is partially exfoliated, the inner layer 

 preserves the longitudinal, and to some extent the transverse striae, in a very 

 subdued condition. 



The internal cast is essentially smooth, with the sutures distinctly 

 impressed, and the substance of the filling strongly imbricating. Sometimes 

 there are thin films of the macerated test remaining attached, which par- 

 tially preserve the surface-markings; and the cast often retains distinct 

 impressions of the revolving striae of the inner, nacreous layer of the shell. 



