308 HELICID^E. 



ing in action a curved or wavy motion, or undulation, 

 commencing at the extremity, proceeding rapidly for- 

 ward, and terminating at the head. But before one 

 muscular wave is exhausted at the head, another has 

 begun to flow ; so that two series of undulations are 

 visible at one time. With this double alternation of 

 action, the body is propelled with a rapidity greater 

 than can be attained by the more common, gliding motion 

 of the Helices. During motion the tentacles are ex- 

 tended, and remain steadily in one position. 



They are found in woods, on the ground, under 

 leaves, but are not very plentiful. The most northern 

 point where they have hitherto been noticed is Tampa. 

 On the eastern shore of the peninsula, they occur at 

 Cape Florida, and also at Key West and Key Biscayne. 



[The great similarity of this shell to P. unicarinata 

 of Lamarck and Cylindrella Grossei, Pfeiffer, would at 

 first throw some doubt on the propriety of regarding it 

 as a distinct species. Compared with the former, it is 

 smaller, has more whorls, a more complete aperture pro- 

 jecting to the left side, and is still more remarkable for the 

 crenulated suture produced by the projection of every 

 second rib. It is larger than C. Cf-ossei, and very differ- 

 ently colored. Dr. Binney, with much doubt, called it 

 P. unicarinata; and it is regarded as a Pupa in the 

 tables of the Introduction ; but, on further consideration, 

 it is clearly to be placed in the genus Cylindrella, hav- 

 ing all its peculiarities. [G.] 



