m 



50 A MANUAL OF AMERICAN LAND SHELLS. 



(c) We next find the same arrangement as in the last, but with the 

 Fig. 9. change from laterals to marginals made 



f— J by the splitting of the inner cutting point, 



37 which continues to the extreme marginals. 



' '7 "^ Of such I figure that of Arionta Dlabloen- 



Linsrnal dentition of Arionta • 



I>iahloensUi. SIS. 



{(}) We then have the form of dentition characterized by tricuspid 

 Fig. 10. centrals, bicuspid laterals and marginals, 



as in ArioUmax HempMlU., all with cutting 

 points. 



(e) Again, with centrals and hiterals as 



Lingual dentition of .4 rioHmax 



Eemphiiii. ill the last, we have the form which is char- 



.acterized by having the inner cutting jjoint of the marginals bifid. Such 



Fig- 11- is Folygyra leporina, here figured. The 



X^ c^^ outer cutting point in the extreme mar- 



ginals is also bifid. 



When the dentition of any genus is dif- 



Lingual dentition of Folygyra le- „ , „ A^ , n r. i, , , 



porina. icreut Irom that of any of the above types, 



:a figure of its dentition is given in the text. 



F'^- ^^ °'- The usual type of lingual mem- 



brane furnished with aculeate 

 marginal teeth is shown in the 

 ^^^j^(D4/->v^ V i/ ■"' accompanying figure of that of 



Lingual dentition of Yitrinizonites latissimus. T^itvinizonitdS lutissiMUS. 



v.— CLASSIFICATION. 

 Order PULMONATA. 



Lingual membrane varying from short and broad to long and nar- 

 Tow ; teeth numerous, in numerous uniform transverse rows. Mouth 

 usually with one or more horny jaws. Eespiratory organ in the form 

 of a closed chamber lined with pulmonic vessels on the back of the 

 animal and covered by the shell when present j edge of the mantle 

 attached, the entrance to the air-chamber being through an opening 

 in the side, closed by a valve. Operculum almost universally absent. 

 Animal hermaphrodite, with reciprocal impregnation, generally ovi- 

 parous, terrestrial, fluviatile, or marine, but respiring free air. Tenta- 

 cles and eye-peduncles retractile or contractile. 



Shell varied in form, sometimes rudimentary or wanting. 



