The mantle {a. pi. I. 2. 3. & 5.) is attached to the posterior part of the 

 head ; but prior to being continued over the back of the animal, it is produced 

 into a considerable fold (b. pi. 1. 2. & 3.). This fold is concave posteriorly, 

 and overlaps the involuted convexity of the shell, which thus becomes coated 

 with a layer of naker, and probably also receives from this part of the mantle 

 the black stain which is usually observable upon it. The sides of the fold extend 

 over the umbihcus, obliterating it on both sides by successive depositions of 

 naker. This fold is composed of two layers of the mantle firmly adhering 

 together, except at the commencement, where it is thinnest, and where the layers 

 are partly detachable from each other ; the rest of the fold is muscular, and 

 of the thickness of a shilling. The anterior margin of the mantle (c. pi. 1. 

 & 2.) is continued downwards and forwards on either side, free and unattached 

 to the parts beneath. The mantle was thickest at this part, doubtless from 

 being in a state of contraction, but, like the mantles of the Conchifera, it can 

 probably extend beyond, and be reflected over the anterior margins of the shell. 

 At the ventral aspect of the body the mantle becomes thinner, is prolonged 

 anteriorly, and is perforated by a large aperture {d. pi. 1.), through which the 

 funnel passes. 



About an inch behind this aperture there are two circular convexities {e. e. 

 pi. 1. & 2 ; b. pi. 5.) ten lines in diameter, firm to the touch, and indicating a 

 thickening of the mantle at this part ; they might be mistaken for the muscles 

 of attachment, but are occasioned by a glandular apparatus (c. pi. 5; fig. 8. pi. 8.), 

 hereafter to be described, attached to the inner surface of the mantle, and which, 

 if not peculiar to, is in all probability more strongly developed in the female 

 than in the male Nautilus Pompilius. 



Behind these eminences the mantle is encircled by a thin layer of brown 

 horny matter, readily detachable from the membrane itself. This belt (/. pi. 1 .) 

 is about a line in breadth at the dorsal and ventral aspects of the body ; but at 

 the sides it exjaands into a broad patch (g. pi. 1.), of an irregular oval form, 

 convex anteriorly, and measuring about sixteen fines in the long, and nine in 

 the short diameter. The horny matter is also thicker here than at the narrower 

 parts of the girdle, and is divisible into several laminse, which form the medium 

 of attachment and, as it were, the tendons of the muscles adhering to the shell, 

 {I. I. fig. 2. pi. 3.) ; to which, indeed, they are so firmly attached, that when, in 



c 



