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 (/, /, /', i) has its anterior part of a more thick and fibrose texture and a 

 yellowish colour ; the posterior part (i) forms a thin and nearly transpai'ent membranous 

 sac, containing the different viscera. The free sujjerior margin of the mantle ascends 

 behind the hood (/') 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 (g), 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 whole mantle, separates its poste- 

 rior soft part or the visceral sac {i) 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 (j) was concealed in the lower and posterior part of the termi- 

 nating 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 



' 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 palceonto- 

 graphs as Aptychus, were two shelly supports of the hood of Ammonites, extinct Ccphalopods not very different 

 in structure from the Nautilus, and belonging, like that genus, to Prof. Owen's tetrabranchiate group. 



