CONCHOLOGIA CESTRICA. 6l 



Shell very small, cylindrical, tapering at both ends, 

 white, shining; whorls 5-6, very oblique; 

 aperture oblique, oval, with a plait, on the c ' 

 columella, and a slight one near to the open 

 umbilicus; lip thick, reflected, and flattened; 

 lingual membrane with the rows of teeth 

 slightly bent; buccal plate plain, slightly 

 arched. H. i^, W. ^, mill. 



Lingual Dentition of C. exiguium. [Morse.] 

 Fig, 115, 



Station, among chips, moss, etc., almost in the water. 

 New Garden, Chester County ; frequent. 



Family LIMNAEID^. 



Shell variable, thin, horn color, usually with a slight 

 fold on the columella ; lip simple, acute. 



Animal, muzzle short, broad, dilated ; tentacles con- 

 tractile, flattened, subulate; eyes at their inner base; 

 respiratory orifice on the right side. 



Station, fresh water ; rising to the surface to breathe. 



OBS. The Limnaeidce are generally sluggish animals; 

 often preferring stagnant pools to clear running streams. 

 They are herbivorous, feeding on the small confervoid 

 plants which everywhere abound, in places which they 

 inhabit. 



Their breeding season commences in the spring, and 

 extends to midsummer. During this period, they are 

 more readily found, and captured. In early autumn, 

 they fill the pulmonary cavity with air, and soon disap- 

 pear beneath the mud ; still penetrating deeper, as the 

 cold increases. 

 6 



