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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Two group.s situated upon either .side of the l)uceal cone, and nearly meeting dor.sally, are 

 the superior labial tentacles. (Fig. 5, SLL; Text-fig. 2, SLL.) Two other groups, situated below 

 the buccal cone but wrapping around it laterally, are the inferior labial tentacles. (Fig. .5, L; 

 Te.xt-rig. 2, ILL.) 



The superior labial tentacles project from two broad, flat, thin loljes which arise from the 

 base of the inner side of the cephalic sheath. The lobes are about 3 centimeters broad and 2 

 centimeters high. From the ends of the lobes low ridges are continued; dorsally to unite the 

 two, ventrally to end above the funnel near the innermost digital tentacle of each side. (Text- 

 fig. 2.) One might say that these two lobes are only local elevations of a single ridge 

 which nearly surrounds the mouth parts. The upper edge of each lobe is subdivided into a 

 number of more or less separate processes. The tip of each process is free for from ti to 10 

 millimeters, while grooves upon l)oth surfaces of the lobe indicate a division for some distance 

 farther back. At the tip of each process is an opening leading into a cavity li to 2 centimeters 



Text-fig. 2.— Diagram of the arrangement of the tentacles of the female nautilus, viewing them from the front. 



B, buccal ma-fs. CS, cephalic sheath, composed of the fused sheaths of the digital tentacles. ILL, inferior labial lobe. .SLL, superior 

 labial lobe. 1, 2, 3, 4, a series of four small digital tentacles upon the otUer side of the cephalic sheath. 



deep; each projection is the free end of the sheath of the cirrus which projects through its opening. 

 Thus the superior labial tentacles have the .same principal structures as the digital tentacles. 



The numl)er of tentacles in the superior labial group is very variable within certain limits. 

 The most ordinary number is twelve in each group; as few as ten, or as many as fourteen are 

 quite common. Rumph (ISO;")) counted sixteen in each group. The number is usually, but not 

 neces.sarily, the same in both groups of one individual. I have not, however, found a difference 

 of more than one. 



The arrangement of the tentacles seems to be constant. As is .shown in the diagram (Text- 

 fig. 2) there is an inner row of nine, and, at about the middle of this, an outer row of three. 

 The variable tentacles seem to be at the ends of the longer row, the shorter row having always 

 been found to be normal. 



