CYLINDRELLA. 307 



ribs across it ; aperture roiinded, oblique ; lip thin, 

 somewbat reflected ; axis impressed, not truly perforate. 

 On the last whorl, a colored line revolves : this is some- 

 times raised a little from the surface, and sometimes is 

 sharp like a delicate carina. , 



Extreme length half an inch ; extreme diameter one- 

 fifth of an inch ; ordinary size less. 



Geographical Distribution. Inhabits the southern 

 part of East Florida and the adjacent islands, also the 

 island of Cuba. 



Remarks. Its numerous, tumid whorls, agreeably 

 marbled, and its crenulated suture and graceful form, 

 render this a very pretty species. It differs entirely 

 from any other North American shell ; but belongs to a 

 group peculiar to the West Indies, of which there are 

 now several species known. 



When in motion, the axis of the shell is parallel with 

 the line of progress, and lies almost horizontally. The 

 rapidity with which the animal moves is quite surprising. 

 The advance seems to be efiected in this way. The pos- 

 terior point of the disk of the foot, being detached from 

 the object on which it rests, is carried forward by mus- 

 cular contraction and again fixed, leaving a curve be- 

 tween the attached point and the next anterior part of 

 the disk, which is not yet detached. This operation is 

 continued throughout the whole disk, every part of which 

 becomes successively detached, curved upward, and 

 again attached, from the extremity to the snout, exhibit- 



