MOLLUSCA. 827 



geniculate curvature, its greatest transverse diameter below the 

 outer angle of the horizontal portion a little within the point 

 from which rises the margin of the hood-like aperture; beyond 

 this point the diameter decreases more or less rapidly to the aper- 

 ture; number of inner coils not determined, broadly rounded on 

 the ventral side, their dorso-ventral diameter less than the trans- 

 verse when not distorted, closely coiled, the umbilicus very small ; 

 from the last septum the dorsal margins of the living chamber 

 rise abruptly in a straight line from the umbilicus to a point 

 beyond the venter of the second volution and then again curve 

 forward at nearly a right angle; the ventral margin has nearly 

 the same direction as the dorsal, but the lower portion of the 

 living chamber is not so nearly vertical and the curve to the for- 

 ward direction is longer. Surface of the shell, to the beginning 

 of the living chamber, marked with rather sharp transverse ribs 

 which continue around the shell from umbilicus to umbilicus, 

 increasing by division and intercalation at about the middle of 

 the sides of the shell where there is a more or less indistinct row 

 of small nodes; upon the lower vertical portion of the living 

 chamber the transverse ribs become more remote and are nearly 

 obsolete upon the sides of the shell beyond the row of nodes which 

 become gradually more conspicuous towards the aperture ; at the 

 geniculate curve of the venter of the living chamber the trans- 

 verse ribs again become more approximate, and so continue to 

 the aperture; they do not, however, continue across the sides 

 of the shell beyond the row of nodes ; near the dorso-lateral mar- 

 gins of the living chamber just opposite the geniculate curve, 

 there are two rather strong nodes on each side of the shell, the 

 ones farthest from the aperture being the largest nodes upon the 

 shell and through which is the greatest transverse diameter of 

 the shell. Sutures comparatively simple, with a ventral and three 

 lateral lobes; the ventral lobe with a broad, rounded siphonal 

 saddle and two secondary lobes on each side, the lateral lobes 

 becoming successively smaller and less complicated to the um- 

 bilical margin; the first lateral saddle broad with three major 

 divisions, each of which is bifid ; the second lateral saddle deeply 

 bifid, the third simple or very slightly bifid; the larger indenta- 



