XArXlLIDJE. 
3G3 
met with in the Jurassic and Cretaceous rocks of England which, 
so far as I am aware, have not yet been illustrated h 
The Ehyncholites, like the Aptychi of the Ammonites, are found, 
as a rule, isolated, so that their connection with any given species 
is largely a matter of conjecture. 
There seems ample justification for the conclusion that lihyn- 
cholites Jiirundo, Eaure-Biguet, and Concliorliynchus avirostris 
Schlotheim, sp., are, respectively, the upper and lower mandibles of 
Temnocheihis bidorsatus of the Muschelkalk of Bavaria, &c. Eur- 
thermore, the beaks of a Sautilus — N. Libanotieiis, Eoord and G. C. 
Crick" — from the Upper Chalk of Lebanon, Syria, are preserved 
in situ (see fig. 82). There are thus two forms of fossil Eautiloid 
beaks which may be compared with those whose affinities have not 
yet been established^. 
Before presenting figures of some of the mandibles of fossil 
Cephalopods in the British Museum collection, I give here (fig. 76) 
figures of the detached mandibles of Nautilus pomi)Uius for com- 
parison with the former. In addition to these I have copied 
(fig. 77) part of Sir II. Owen’s figure on plate iv. of his ‘ Memoir on 
the Pearly Xautilus,’ showing the mandibles in their natural posi- 
tion, by which their relation to the buccal mass and surrounding 
parts may be better comprehended. 
Sir II. Owen^ thus describes these mandibles : — “The calcareous 
extremities of both mandibles are of a liardness apparently adequate 
to break through the densest crustaceous coverhigs, or eveji shells 
of moderate thickness. That of the upper mandible is sharp- 
pointed, and solid to the extent of five lines from the extremity ; 
but in the lower one the calcareous matter is deposited on *both 
sides of a thin layer of the black horny substance, and thus a com- 
bination of tough with dense matter is obtained, which much 
diminishes the liability to fracture. This mandible is also more 
hooked than the upper one, but is more obtuse at the end : it 
^ "VTith the exception of those figured in a very sketchy manner by Buckland, 
from imperfect specimens. See Bridgewater Treatises — Geol. and Min. 1837, 
vol. i. p. 319; Aol. ii. p. 53, pi. xxxi. figs. 5, 6. Mantell’s figui es are merely 
outlines; see ‘Medals of Creation,’ 1844, vol. ii. p. 478, woodcut 105, figs. 1, 
la,\h. 
^ See supra, p. 304. 
^ Buckland (Bridgewater Treatises — Geol. and Min. 1837, vol. ii. p. 54, 
footnote) remarks that he possessed “a specimen of a fossil Nautilus horn the 
Lias at Lyme Begis, in which the external open chamber” contained a 
Bhyncholite. 
‘Memoir on the Pearly Nautilus,’ 1832, p. 21, pi. viii. figs. 2-5. 
