xautilidj:. 
3 Go 
8i), a and e; 82; 83,6) will not be disputed. There seems to be, 
therefore, sutficieiit evidence upon whicli to rest the assumption 
that the fossil mandibles referred to belonged to the genus Xautihis. 
They do, indeed, vary in detail ; but such variations may be sig- 
niticant of specific, rather than of generic differences in the animals 
to which the beaks belonged, or they may be due simply to 
ditference in age. There is still much force, however, in Buck- 
land's ^ contention that ‘‘ although the resemblances between these 
Fig. 77. 
Xaiitilus poinjpilius. — a, part of the hood, or upper part of the oral sheath, 
longitudinally divided and turned back ; e, e, the cut surfaces of tlie 
same;/,/, the internal surface of the oral sheath; g, g, the external 
labial processes; h, h, the external labial tentacles; i, i, the internal labial 
processes ; k, k, the internal labial tentacles ; I, the olfactory laininaa ; 
m, //i, the circular fringed lip, longitudinally divided ; n, the upper man- 
dible ; 0 , the lower mandible ; p, the muscular basis on which the mandibles 
are fixed ; q, q, tlxe superior pair of muscles which retract the jaws; r, r, 
the semicircular muscle which protrudes the jaws, divided longitudinally. 
Copied from pi. iv. of Owen’s ‘ Memoir on the Pearly Nautilus ’ (1832). 
fossil beaks, and that of the animal inhabiting the N. ptompiliiis, 
are such as to leave no doubt that llhyncholites are derived from 
some kind or other of Cephalopod, yet, as they are found insulated 
in strata of Muschelkalk and Lias, wherein there occur also the 
remains of Sepia) that had no external shells, we have not yet suffi- 
cient evidence to enable us to distinguish between the Bhyncholites 
derived from naked Sepise, and those from Cephalopods that were 
connected with chambered shells.” This last consideration has, no 
doubt, led some pala)ontologists to describe fossil beaks under 
generic and specific names, with the view of escaping the difficulty 
^ Bridgewater Treatises — Geology and Mineralogy, 1837, vol. ii. p. 54 (foot- 
note). 
