15 



anterior margin ; and each canal contains a tentacle (r. pi. 3 ; h. k. pi. 4 ; h. i. 

 pi. 7.) similar to, but somewhat smaller than those of the external digitations. 

 The canals extend for about half an inch vdthin the substance of the processes, 

 and into some of these canals the tentacles were completely retracted, but most 

 of them were protruded ; the middle ones for the extent of an inch, the rest 

 diminishing in length on either side : those of the inferior processes were found 

 to be applied immediately over the orifice of the mouth, the left tentacles over- 

 lapping and concealing the right. 



The inferior labial processes are about an inch in length, and ten lines in 

 breadth ; the superior and external ones are broader, but shorter : they are of 

 equal thickness, viz. about two lines throughout, and are concave towards the 

 mandibles. Their surfaces, both external and internal, are smooth and lubri- 

 cated, and are covered by a fine membrane, which is reflected from the inner sur- 

 face of the sheath, and afterwards continued from them upon the circular lip 

 which immediately surrounds the mandibles. The structure of the labial ten- 

 tacles is the same as that of the digital ones ; but they are somewhat smaller, 

 softer, and of a whiter colour. 



With the external description of Nautilus Pompilius should be included the 

 peculiarities of the shell ; but the few observations that require to be added on 

 that subject will be given in another part of this Memoir. 



From what has already been said, it will be seen how considerable are the 

 external differences between the Pearly Nautilus and the higher Cephalopods ; 

 nevertheless, its general plan of organization renders its claim to rank with 

 them indisputable ; and as its locomotive apparatus is confined to the head, the 

 received denomination of the class remains undisturbed by its admission. 



Tlie inferior or ventral pair of labial processes I consider as analogous to the 

 superadded pedunculated arms of the Cuttle-fish and Calamary, which also come 

 off more internally than the shorter arms, and are approximated or united at 

 their bases on the ventral aspect of the mouth. The other pair in Nautilus 

 appear to result from a higher degree of organization of the part analogous to 

 the external lip in the preceding genera. The curtailed digitations are, how- 

 ever, but feeble representatives of the elongated and cotyligerous arms of the 

 Poulp or Cuttle-fish ; and the retractile tentacles, pedicellate eyes, and flattened 

 disk, which according to the testimony of Rumphius is applied to the ground 



