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 striae 
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 
