3 
sac (i) from its free and thicker anterior part. The thin and mem¬ 
branous posterior part of the mantle is of a bluish white colour, but 
being imperfectly transparent, it seems to be dark at all places where 
it covers the bulky liver, whose colour is a dark red-brown, or choco¬ 
late-like purple. At the inferior part of the free portion of the mantle 
is a convexity (A), where lies a glandular laminated organ, secreting, 
as it seems, a covering to the eggs, and which projects at this place, 
being partly visible through the integuments. This glandular mass 
connected with the female generative system is situated behind the 
gills, at the inner surface of the mantle. 
A more complete idea of the external form of the animal may be 
had by comparing the two following figures. Fig. 2 represents the 
animal taken out of the shell from a dorsal aspect. The circumference 
appears oblong, and of an irregular oval form. The whole is divided 
into two chief parts ; the first is the hood, exactly filling up the shell’s 
aperture * ; the second part was concealed in the lower and posterior 
part of the terminating chamber of the shell. The dorsal fold (/') 
appears now wholly visible; it forms a thin lamellar production of 
the mantle, and ascends to the protuberant internal labium or anfrac- 
tus of the revoluted shell. Hence the upper surface of this fold is 
excavated, forming the exact counterpart of the shell’s protuberance. 
Under that fold is a smaller plate of nearly the same form, but adhe¬ 
rent to the posterior declivous surface of the hood, and only free at 
its circumference. This plate is of an aponeurotic texture and a white 
colour : at both sides it is united to the dorsal fold, and below it seems 
to have an intimate connexion with the two side parts of the funnel, 
and indeed to be a continuation of those parts. The dorsal or superior 
part of the aponeurotic band, which forms, as we have said already, 
the continuation of the oblong side-plate (fig. 1 g), is here visible at 
g , g • Three small longitudinal bands or tendinous inscriptions (A, A, A) 
seem to give some firmness to the dorsal part of the abdominal por¬ 
tion of the mantle. Near the posterior end of this visceral sac, nearer 
however to the superior surface of it, is the beginning of the siphon 
(j) ; it seems nearly superfluous to say that this siphon is a tubular 
production of the visceral part of the mantle, protected by a calcareous 
covering, and penetrating by the central perforation of the several 
septa in all the following compartments of the shell. 
At the inferior surface (fig. 3) a part of the funnel is visible in 
the middle of the digitations of the head. The inferior face of those 
digitations is o'f a white colour, contrasting with the brown and dark 
colour of the hood and of the superior surface of the digitations which 
are nearest to it. The free inferior and anterior margin of the mantle 
appears rounded and somewhat convex ; it conceals the basal part of 
the funnel and of the appendages of the head. 
More instructive is an inferior view of the animal if the mantle has 
* It may be allowed to hazard here the opinion, that the two juxtaposed fossil 
shells, known by palfeontographs as Aptychus, were two shelly supports of the 
hood of Ammonites, extinct Cephalopods not very different in structure from the 
Nautilus, and belonging, like that genus, to Prof. Owen’s tetrabranchiate group. 
