HELICTD^. 



25 



one strongly developed, situated on the under side of the upper 

 septum, and in length about equal to one-half of the circumference 

 of the whirl ; another on the upper surface of the lower septum, 

 immediately beneath and opposite to the above-mentioned lamella, 

 and of about equal length, but not bo much developed ; a third 

 lamella on the middle of the lower half of, and revolving on the 

 axis ; the fourth on the inner side of the outer wall of the shell 

 (opposite the axial lamella), and visible from the exterior, (Bland.) 



Spurious Species op Cylindrella. 



Cylindrella pontijica, Godld, is Macroceramus kieneri, Pfe. 



Family HELICID.^. 



Lingual membrane with numerous similar, transverse 

 rows of teeth. 



Jaw smooth, striated or ribbed, with or without a centjal 

 projection on its concave margin, single, or composed of 

 numerous separate plates. 



Body elongate, attached its whole length to the upper 

 surface of the foot, or more or less spiral and prominent 

 on the middle of the upper surface of the foot. Eyes at the 

 end of long, cylindrical, retractile peduncles; tentacles 

 shorter, retractile, sometimes wanting. Mantle thin, small, 

 diseal or spiral, on the middle of the back ; respiratory ori- 

 fice subcentral, on the right side. Foot narrow, elongate, 

 without a distinct locomotive disk, simple posteriorly. Vent 

 near the respiratory orifice, central. Orifice of reproductive 

 organs usually below the respiratory orifice or behind the 

 right eye-peduncle. 



Shell very variable in form, sometimes rudimentary and 

 internal. 



Subfamily YITRININ^. 



Jaw smooth, usually neither striated nor ridged, with a blunt 

 middle projection. 



