MELAMPUS. 469 



across at about the anterior third ; tentaciila slender and tapering, 

 the eyes at the inside of the base ; rostrum nearly as long as the 

 tentacula, with an expanded lol)e each side. 



The perfect shells are smooth and brown, with usually three or 

 four darker, narrow l)ands ; but the shells soon become eroded, and 

 the surface is left rough, and of a grayish color. The ridges within 

 the outer lip arc not seen except in aged shells. 



Say designates by the name of /meatus a form peculiar for its re- 

 volving lines or bands and more narrow base of the ajjerture {vide 

 Binn. ed. p. ,85). I have met with none sufficiently marked to form 

 a variety, much less a distinct species. The revolving lines are 

 commonly found on young specimens. De Kay mentions this as 

 var. a, Pfeiifer as /S. 



Stimpson gives precedence to Deshayes's name corneus. Say's 

 name has eight years' priority, and is not preoccupied in the genus 

 Melampus. It was while treated as an Auricula that any question 

 existed in regard to its specific name. 



Family LIMN.EIDiE. 



Lingual membrane armed with numerous, quadrate teeth, ar- 

 ranged in transverse rows, the central minute, the laterals unci- 

 nated or simply denticulated. Head with a broad, short muzzle, 

 dilated at the end ; mouth with one or more jaws ; tentacles con- 

 tractile, flattened or subulate, with the eyes sessile at their inner 

 bases. Mantle margin variously modified ; respiratory orifice at 

 the right side. Foot flattened, lanceolate or ovate. Excretory ori- 

 fices on the left side of the neck. Sexes united ; male and female 

 organs with separate orifices, on the right or left side. 



Shell of a varied form, thin, horn colored, usually with an oblique 

 fold on the columella, and with the outer lip simple and acute. 



Animal living in fresh water, usually coming to the surface to 

 respire the free air. 



The Limnccidcc are found in every quarter of the globe ; but in 

 North America most of tlie genera are represented, excepting Chil- 

 ina, Camptocerns, Amphipep/ea, Latia, &c. They are more plenty 

 in species and indivi(hials in tlic more temperate portions of the 

 continent. Especially among the innumerable lakes of the British 

 possessions do the large species flourish. 



