CiECUM. 155 



part of his body lies straight up in the tube, or whether it 

 is twisted through a spiral curl to the apex. 



The indefatigable Mr. Clark has discovered and lucidly 

 explained the true nature of the Ccecunij which has a spiral 

 shell in its extreme youth, and has also the curious habit, 

 in common with the Tiirritellay of partitioning off a chamber 

 in the upper part of the hollow, by building a septum across 

 it. In Tarritella the deserted part of the spire beyond this 

 septum remains, in Ccecum it falls off. 



The Ccecum carries a horny, round, spiral operculum, 

 with many plain-edged whorls, thus, in another respect, as- 

 piring to an affinity with the more noble Turritellaj the 

 head is muzzle-shaped, with long slender horns, having the 

 eyes in their base ; the foot is short, squarish in front, and 

 rather blunt behind ; the mantle has no fringe. Mr. Clark, 

 who watched the movements of living specimens with great 

 perseverance, after minutely describing the characters, says : 

 ^' The animal is not at all shy; it shows itself in all directions, 

 marches with great vivacity, carrying its shell sometimes 

 with the convexity upwards, resting on the posterior point 

 of one of its sides, frequently changing one for the other, 

 by suddenly withdrawing the head and body, by which ac- 

 tion it is thrown on the operculum at an elevation of fifty 

 or sixty degrees ; it then turns on the side it wishes." 



