22 VAN DER HOEVEN ON THE ANIMAL 
together with a part of the three following compartments. The hood (a), composed 
according to Professor Owen by the conjunction in the mesial line of the two superior, ex- 
cessively large digitations, covers with its projecting margin the superior surface of the 
pedunculated eye (6). The inferior half of the eye is concealed by the superior margin 
of the mantle, which covers also the greatest part of the digitations or lateral processes 
of the head (c, c). The extremity of the funnel (d) is visible and uncovered, the rest 
being contained in the anterior part of the mantle. There is no perforation or excision 
at this part of the mantle’, but the margin of it is entire and slightly convex. 
The mantle (f, f, f’, i) has its anterior part of a more thick and fibrose texture and a 
yellowish colour ; the posterior part (2) forms a thin and nearly transparent membranous 
sac, containing the different viscera. The free superior margin of the mantle ascends 
behind the hood (f') and forms the dorsal fold of Professor Owen’s memoir ; but at the side 
view only a small portion of this fold is visible. Beneath the posterior part of the hood, 
the mantle offers on each side a large aponeurotic flat piece (9), of a bluish white colour 
and a kidney-like shape, being convex at its anterior side and somewhat concave at the 
posterior border. This plate is the posterior insertion of a strong muscular mass—the 
great muscle of the shell—which goes from this attachment in an oblique course, con- 
verging with that of the opposite side, to its anterior termination at the cartilage of the 
head. From this oblong patch arises a narrow aponeurotic stripe, both at the superior 
and at the inferior extremity of it. The oblong plate may be considered as an expansion 
and development of this band, which, encircling the whcle mantle, separates its poste- 
rior soft part or the visceral sac (7) from its free and thicker anterior part. The thin 
and membranous 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 chocolate-like purple. At the inferior part 
of the free portion of the mantle is a convexity (h), 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 (a) is the hood, exactly filling up the shell’s 
aperture* ; the second part (?) was concealed in the lower and posterior part of the termi- 
nating chamber of the shell. The dorsal fold (f') appears now wholly visible ; it forms 
a thin lamellar production of the mantle, and ascends to the protuberant internal labium 
* Professor Owen speaks of a large aperture through which the funnel passes. (Memoir on the Nautilus, p. 9.) 
* It may be allowed to hazard here the opinion, that the two juxtaposed fossil shells, known by palzonto- 
graphs as Aptychus, were two shelly supports of the hood of Ammonites, extinet Cephalopods not very different 
in structure from the Nautilus, and belonging, like that genus, to Prof. Owen’s tetrabranchiate group. 
