^^8 Mr, Home's Defcription of 



pln.kifh white colour : its outer fnrface is covered by the brain- 

 ilone in which it is inclofed, and the turnings and windings 

 which it makes are very numerous, The end of the (hell, 

 which opens externally, riles above the furface of the flone on 

 one fide half an inch in height, for about half the circum- 

 ference of the aperture, bending a little forw^ards over it, and 

 becoming narrower and narrov/er as it goes up, terminating at 

 laft in a point jufl: over the center of the opening of the fhell ; 

 on the other fide it forms a round margin to the furface of the 

 brain-ftone. This part of the fhell is much thicker and 

 Ibonger than that part which is incloied in the brain-ftone : its 

 outer furface is of a darkifh brown colour; its inner of a 

 plnkifh white. 



The animal, when at reft,, is wholly concealed in its fhell ;. 

 but when it feeks for food, the moveable fhell is puihed flowly 

 out with the cones and their membranes in a coUapfed ftate ;. 

 and when the whole is expofed, the moveable (hell falls a little 

 back, and the membrane round each of the cones is expanded,, 

 the tentacula at the hafes of the cones having jufl room enough 

 to move without touching one another. The thin membrane 

 which lay between the cones and the inclofmg (hell is pro^ 

 truded in the form of a fold, and lies over the external (hell 

 which projedls from the brain-ftone. 



The membranes have a flow fpiral motion, which continues 

 during the whole time of their being expanded ;. and the ten- 

 tacula upon their edges are in conftant acflion. The motion of 

 the membrane of the one cone feeras to be a little different 

 from that of the other, and they change from the one kind of 

 motion to the other alternately, a variation in the colour of 

 the membrane at the fame time taking place, either becoming 

 a (hade lighter or darker ; and this change in the colour, while 



the 



