LIMN^A. 



Fig. 81. 



Limncea 



Limnaea catasCOfJium.— Shell thin, horn-color, red, or black- 

 ish ; whirls four or five, the first large and generally the remainder darker 

 and rapidly decreasing to an acute apex and wrinkled across ; aperture 

 large, oval, not three-fourths the length of the 

 shell. Length seven-tenths of an inch ; breadth 

 nearly one-half of an inch. 



Inhabitant yellowish, sprinkled with small, 

 often confluent, paler dots ; teutacula two, broad, 

 pyramidal ; eyes black, placed at the base of the 

 tentacula ; tail obtuse, rounded or emarginate, 

 not so long as its shell. PI. 2, fig. 3. 



It is with much hesitation that we adopt a new 

 catascopium. specific name for this shell, having always hereto- 

 fore considered it the same as the L. putris of 

 authors (which has been, perhaps, mistaken for the Helix linosa of 

 Linne). As far as we can ascertain, the principal difiference appears to 

 be in the more oblique revolution of the whirls in the European species, 

 and the more abrupt termination of the spire. 



Inhabits the Delaware River and many other waters of the United 

 States, in considerable numbers, and may be found plentifully, during the 

 recess of the tide, about the small streams through which the marshy 

 grounds are drained, in company with several other shells. When kept 

 in a vessel of water, like others of its kind, it will proceed not only up the 

 sides of its prison, but also along the surface of the water, the shell down- 

 ward, with regularity of motion and apparent ease. In this ckse the re- 

 verted base of the animal is concave ; and as the- surface of the water is 

 compelled to a corresponding concavity, the pressure of the atmospheric 

 column will account for the sustentation of the animal (whose specific 

 gravity is much greater than that of the water) in this 

 singular position. It occasionally crawls to the margin of 

 the water to inhale a supply of air; with this object the 

 foramen is protruded to the surface, and opened with an 

 audible snapping sound, similar to that produced by the re- 

 silience of the nib of a pen. 



Its European analogue is the L percgruvi, L., from which 

 it may be distinguished by a deeper fold of the columella, l. catascapium. 



Fig. 82. 



