ANCYLUS. 13 'J 



Lingual membrauc broad ; teeth croM'ded, numerous ; central 

 Fig. 231. 



Lingual dentition of Ancyhis nemherryi. 



minute, narrow, simple ; laterals broad, bicuspid, the inner cusp 

 the lai'ger. 



The Ancyli and Arcroloxi are widely distributed over the 

 globe. In North America the known species are most numerous 

 in those States where conchological observations have most been 

 made, but an equal number may be found in other regions when 

 they come to be explored. Thcj are found in the extreme north 

 and in Mexico, at every station.^ 



The name Ancylus is universally adopted at the present time. 



The shell of Ancylus is dextral, the apex being directed to the 

 right, but the generative, respiratory, and anal orifices are on the 

 left of the animal, as in Planorhis. 



So slight are the points of specific distinction in the species of 

 this genus, and so meagre is the material at my disposition, I 

 have considered it best at present to give all the descriptions of 

 species yet published, leaving the synonymy to be decided upon 

 at another time. 



AucylllS o'bscuriis, Haldeman. — Shell ovate, somewhat elevateti, 

 rather wide, apex but slightly projecting, rather more than 

 one-third of the shell posterior ; lateral margins slightly Fig. 232. 

 convex ; lateral slopes rectilinear ; posterior slope with a 

 very slight depression ; anterior slope nearly rectilinear. 

 Color dark brown, margin diaphanous. Dimensions : long. 

 5, lat. 3.-5, elev. 1.5 mill. Found in Nolachuoky River, below 

 Greenville. [Haldeman.) 



Ancijhis obscurus, Haldeman, Mon. 9, pi. i, f. 5 (1S44). 



Adams quotes it from Jamaica (Contr. to Conch. 50) ; Shuttle- 



' Dr. J. G. Cooper found them 7100 feet above the sea on the Sierra 

 Nev da. 



