19 



Genus 3. NAUTILUS, Aristotle. 



Animal ; body forming an oblong mass a little compressed at the 

 sides, the upper half enclosing the head and muscular portion, 

 the lower half the soft and visceral portion, contained in a 

 thin bag-like mantle, rounded at the base in a manner adapted 

 to the cavity of the shell, encircled by a horny girdle by 

 which it is attached to the inner wall of the shell, and ter- 

 minating with a central tubular membranous process or artery 

 which passes throughout the siphon of the shell to the nucleus 

 of the innermost chamber. Head at the upper opening of the 

 mantle furnished {according to Oiueu*) with ninety tentacles, 

 thirty-eight digital, four opthalmic, and forty-eight labial. 

 No arms or suckers. Back of the mantle extending into a 

 broad fold, falling back on the black involuted convexity of the 

 shell. Front of the mantle with an opening through which 

 passes the funnel or vent-tube consisting of a thin fleshy sub- 

 stance the lateral edges of which overlap one another. Back 

 of the head surmounted by a dense leathery lid or hood, which 

 being holloio behind appears to fall backwards on the shell, 

 and forwards over the head, closing in the tentacles and all 

 the delicate structures after the manner of the operculum in 

 the Gastropods. Four branchiae. No ink-bladder. 



Shell ; orbicular, consisting of a compressed cone, convoluted, in 

 symmetrical order, in close spiral whorls one over the other 

 upon the same plane ; more or less umbilicated externally at 

 the axis of convolution. Three-fourths of the shell partitioned 

 into chambers, about thirty-five to thirty-eight in number, by 

 thin internally convex septa, in the centre of each of which, 

 is a short siphon or spouted appendage. Inner surface of 

 the shell pearly, outer surface dull white, the involuted portion 

 being painted with conspicuous chesnut-broion fames striking 

 out of the umbilicus, which is sometimes overlaid with matter 

 deposited by the hind fold of the mantle. 



The Pearly Nautilus, as observed in treating of the Cephalapods generally, 

 is an object of especial interest to the Conchologist, on account of it being 



* Iluuterian Lectures, 1843. 



