A MANUAL OF AMERICAN LAND SHELLS. 51 



Ej^es at the end of elongated peduncles or on the head of the 

 animal. 



The Fulmonata are usually divided into three suborders, Geophila, 

 LimnopMla, and ThalassopMla, names derived respectively from the 

 comparatively terrestrial, fluviatile, and marine habits of the animals. 

 These suborders are readily distinguished by the position of the eyes, 

 either sessile or on peduncles, and the characters of the tentacles. 



I have included in this volume only the species of the first suborder, 

 though one species of the LimnopMla, Carychinm exigunm, is truly ter- 

 restrial. It will be understood also that I do not include any gill-bear- 

 ing genus, however terrestrial may be its habits. Thus I omit many 

 genera included in Vols II. and IV of Terrestrial Mollusks of the 

 United States. For these see also Land and Freshwater Shells of 

 I^. A., Parts II and III. 



Suborder Geophila. 



Eyes at the tips of elongated, cylindrical peduncles ; tentacles retract- 

 ile or contractile, cylindrical, shorter than, and placed under, the eye- 

 peduncles, sometimes very small or wanting. Operculum never present 

 in the adult. Animal usually terrestrial. 



The Pulmonata have been developed into their present state so 

 irregularly that no system of classification has been proposed which is 

 at all satisfactory. It is, however, necessary to adopt one in the fol- 

 lowing pages. 



I have followed, therefore, the general arrangement of the Geophila 

 suggested by Dr. P. Fischer (Manuel de Conchyliologie) as far as the 

 grouping into families, because it is the most recent and one of the few 

 which include the naked genera. In treating of genera I still follow 

 the second edition of Albers' " Die Heliceen," by Von Martens, except- 

 ing that I treat his subgenera of Helix as full genera. 



The characters on which generic distinction is founded are the ex- 

 ternal form of the animal, whether slug-like, as in Limax, or snail-like, 

 as in Helix ; the position of the mantle, anterior, central, or posterior, 

 whether naked, inclosing some form of internal shell, or protected by 

 an external more or less developed shell; the presence or absence of 

 longitudinal furrows above the margin of the foot, meeting over a cau- 

 dal mucus pore ; the presence or absence of a distinct locomotive disk 

 to the foot ; the position of the external respiratory and generative ori- 



