PERISTOMATA. MOLLUSCA. PALUDINA. 227 



cylindrical, and so partially in contact as to expose about one 

 half of the cylinder ; the last entirely disjoined from the preced- 

 ing one for at least die half of a revolution ; aperture circular, lip 

 simple and sharp ; on looking at the shell from below, no umbili- 

 cal opening is found ; operculum horny, apex central, elements 

 concentric. Length -f v inch, breadth T 3 V inch. 



Found at Fresh Pond and other ponds, on stones and sub- 

 merged sticks ; and has been for many years in our cabinets 

 marked as a PALUDI'NA. 



Animal very active ; head proboscidiform, half as long as the 

 tentacles, bi-lobed in front, dark, terminated with light ; tentacles 

 rather stout, light drab-colored, with a line of silvery dots on the 

 upper side, over the large, black eyes ; foot, tongue-shaped, as 

 long as the first whorl, dilated into two acute angles in front, light 

 drab-color ; respiratory organ occasionally protruded to half the 

 length of a tentacle on the right side. 



This species is widely distinguished from all other described ones by 

 its minuteness, its color, its elongated form, and its want of an umbili- 

 cus ; of which characters the last two seem to arise from the loose 

 manner in which the whorls are united. 



i 

 GENUS PALUDINA, LAM. 



Shell ovate-conical, whorls rounded ; aperture ovate, acute pos- 

 teriorly, and modified by the preceding whorl, margin simple; 

 operculum horny, origin near one edge, elements concentric. 



PALUDINA DECI'SA. 



Shell sub-conic, thick and strong, olivaceous; whorls Jive, con- 

 vex, covered with minute, revolving lines, eroded at tip; aperture 

 ovate, half the length of the shell, bluish within; umbilicus none. 



FIGURE, see Wood-cut, page 144. 

 State Coll., No. 61. Soc. Cab., No. 1347. 



C6chlea Virginiana e flava viridescens, non fasciata, LISTER ; Conch. , I. 27, f. 27. 



PETIVER; Gazophyl., t. 116, f. 18. 

 Paludina decisa, SAY ; Nicholson's Encyc., (Amtr. J.,) pi. 2, f. 6. Amcr. Conch , 



pi. 10. 

 Paludina limosa, VALINC. ; Recueil d' Obs. de Zool. fyc., par Humb. et Bonpl , ii. 



253. pi. l,f.l. 



