CEPHALOPODA. 475 



Septa strong, the margins thickened and imbricating — a feature more 

 especially shown at the extremities of the acute lobes and at the margins of 

 the peripheral saddle. Their lateral margins, adjoining the inner volutions, 

 are distinctly more advanced toward the aperture than their exterior mar- 

 gins. From their origin at the axis the septa curve somewhat rapidly 

 toward the aperture for a distance of more than one-third the width of the 

 volution, and then somewhat angularly recurving, recede to a point much 

 behind that of their origin at the umbilical margin. From this point they 

 are bent forward at a very acute angle, and in a line nearly parallel to the 

 periphery of the shell, advancing beyond the summit of the preceding eleva- 

 tion ; and curving over the peripheral margin, they are abruptly turned 

 backward, assuming a course parallel to the direction of the volutions, and 

 suddenly contracting to the centre of the periphery, enclose a narrow, 

 linguiform ventral lobe, with its extremity mucronate. This course of the 

 septa describes an angular umbilical lobe, a broad lateral saddle, a deep, 

 acute lateral lobe, and a narrow and much elevated peripheral saddle on each 

 lateral face of the volution. The linguiform ventral lobe, with its mucronate 

 extremity, penetrates almost the entire depth of the adjacent, preceding 

 air chamber, and sometimes reaches even below the anterior limits of the 

 second preceding air-chamber. The suture-lines are strongly impressed and 

 quite conspicuous in all the specimens. 



Siphuncle minute, perceptible only in the mucronate extension of the 

 ventral lobe. 



Test unknown, all the specimens observed being casts of the interior. 

 Surface unknown. 



The internal casts are well preserved, and strongly marked by the suture- 

 lines, which distinctly define the lobes and saddles. The smallest specimens 

 observed have a lateral diameter of about eighteen mm., and the larger ones 

 are about eighty-five to ninety mm. in their greatest lateral diameter. 

 These measurements pertain only to the septate portion, which may be 

 incomplete. 



