

BELOGONA-SIPHONADENIA. 237 



cyclas, and may as readily have belonged to Belogona as to Epiphal- 

 logona, for anything now known ; and while we should not at the 

 present stage of malacology deny the presence in European Eocene 

 and Miocene of genera allied to Obba, Caraeolus (=Pleurodonte) r 

 etc., neither should palaeontologists lightly affirm that " Geotrochus" 

 Obba, Chloritis, etc., exist in European Tertiary, on the strength of 

 mere resemblances of contour and sculpture characters of no sys- 

 tematic value, and now abandoned by all helicologists in studying 

 recent Helices. 



Synopsis of recent genera. 



1. Dart sack 1 ; mucus glands 2 or in 2 clusters ; spermatheca on a 

 very long duct, usually with diverticulum ; shell usually conspic- 

 uously banded. 



a. Jaw with strong, convex vertical ribs ; dentition normal. 

 b. Dart four-bladed ; diverticulum free when present ; 

 shell typically five-banded, Helix* 



bb. Dart two-bladed ; diverticulum always present, united 

 by a wide membrane to uterus ; shell none to three 

 banded, Helicigona. 



aa. Jaw with converging flattened ribs ; dentition normal, 



Leptaxis. 

 aaa. Jaw smooth ; teeth all unicuspid and strap-shaped, 



Allognathus. 



Dart sack 2, 1 or 0, the dart bladeless or two-bladed ; mucus 

 glands 0, 1, or several, rarely more than 2-branched ; spermatheca 

 duct short, with no diverticulum ; shell with many or no bands. 

 a. Right eye-retractor passing between branches of genitalia, 

 shell uuicolored or 1-banded, rather corneous in texture. 

 b. Shell with well-reflexed and thickened lip, often toothed,. 



Helicodonta. 

 bb. Shell with simple or expanded lip, texture corneous, 



aperture lunate. 



c. Depressed-globose or depressed, not laminate, size 

 moderate or small, Hygromia. 



cc. Conoidal, with costate or lamellar riblets ; minute, 



Acanthinu/a. 



bbb. Aperture round, oblique, toothless; shell minute, de- 

 pressed, few-whorled, Vallonia. 



