2 LAND AND FRESH-M'ATER SHELLS OF N. A. [PART IL 



above, separated below ; tentacles subcylindrical, contractile ; 

 eyes sessile at the inner sides of the bases. Mantle closed, 

 with a thickened margin ; foot long, posteriorly blunt ; respi- 

 ratory orifice posterior, on the right side, excretory orifice 

 near it. Sexes united, orifices of generative organs distant, 

 on the right side. 



Shell spiral, covered with a horny epidermis; aperture 

 elongate, with strong folds on the inner lip ; outer lip often 

 dentate. 



Animal usually frequenting salt marshes. 



The Auriculidse are easily distinguished from the other in- 

 operculated air-breathing Mollusks. They are furnished with 

 but one pair of non-retractile tentacles, on the inner base of w^hich 

 are situated the sessile eyes. The head is extended beyond the 

 tentacles into an obtuse, rouuded, bilobed snout. The mantle is 

 thin, thickened on its margin. The foot is elongated and pointed. 

 The sexes are united in each individual. 



The shell is spiral, extremely variable, and in the American 

 species conic, generally with a flattened spire, and furnished with 

 numerous tooth-like laminte, which contract the narrow aperture. 

 The internal septa are usually removed. 



The Auriculidse are amphibious Mollusks, breathing free air, 

 but apparently dependent for existence on a great deal of moisture, 

 if not on the actual vicinity of the sea. Some species pass their 

 whole life under circumstances which seem to preclude the possi- 

 bility of their respiring air. Thus Alexia viyosotis is often found 

 on isolated stones in salt marshes, which are entirely covered by 

 the tide four hours out of twelve. This species, when immersed 

 in fresh water, becomes benumbed and soon dies. 



Garychium exiguum, on the other hand, though found under 

 similar circumstances, does not depend on the proxinn'ty to salt 

 water, being widely distributed far beyond its influence over the 

 interior of the country. Blauncria pdlucida, also, has been 

 detected living far from any water in a garden in the District of 

 Columbia, whither it was introduced on plants from Charleston, 

 S. C. With the exception of the two last mentioned, the Ameri- 

 can species are found on salt marshes and in brackish water near 

 the sea. 



Of the geographical distribution of our species but little is yet 

 known. Melampus bidentatua is found from Maine to Texas. 



