CEPHALOPODA. 445 



Chamber of habitation not fully observed. Aperture similar in form to a 

 transverse section of the volution, and moderately auriculate at the posterior 

 angles. Air-chambers numerous, shallow at their origin, expanding some- 

 what rapidly, and again contracting on the middle of the lateral face, beyond 

 which they are again expanded toward the periphery. 



The septa are thin, with the margins slightly thickened; closely arranged 

 at the axis, and rapidly diverging, having a somewhat prominent saddle, 

 which occupies the inner half of the disc; thence abruptly recurving, they 

 describe a somewhat semi-elliptical curve, which limits the deep, lateral lobe ; 

 and in the retral curving, upon the peripheral margin, include a distinct 

 saddle of semi-elliptical form, and sometimes with a subacute apex. The 

 ventral lobe is narrowly triangular, and penetrates about one-third the depth 

 of the preceding, adjacent air-chamber. The measurements show the eleva- 

 tion of the saddle to be greater than the depth of the lobe, the length of the 

 two being equal. The height of the saddle is equal to the depth of two air- 

 chambers, and the depth of the lobe equal to one air-chamber. In another 

 specimen the height of the saddle is equal to the depth of the lobe, and each 

 equal to nearly the depth of two air-chambers. The width of the saddle is 

 greater than the width of the lobe. The sutures are well defined in the cast, 

 showing an imbrication of the septa toward the aperture. 



The siphuncle is small, and situated close beneath the test, on the ventral 

 side, and distinctly expanding anteriorly between the adjacent septa. In a 

 small individual it measures .5 mm., and in a larger specimen, in the 

 anterior part of the chamber, it is 1.2 mm. in diameter. 



Test thin, having a thickness not exceeding .2 to .5 mm., except where 

 thickened from being replaced by iron pyrites. Surface striated, the stria? 

 having essentially the direction of the septa, and making a moderately deep 

 sinus on the periphery. 



The internal casts are smooth, except the distinct impressions at the 

 suture lines. A single fragment, from which the exterior shell has been 

 exfoliated, shows a peculiar, delicate ornamentation on the inner walls of the 

 air-chambers, consisting of very minute, wrinkled or interrupted striae, which 



