THE NATURAL HISTORY SURVEY. 303 



small lobe; genitalia on the left side; jaws three, thin, lateral 

 plate fused with the superior jaw, ornamented with papillae; 

 lingual membrane broad, with numerous, crowded teeth; cen- 

 tral tooth small, narrow, simple; lateral teeth broad, bicuspid, 

 the inner cusp much the larger and bifid; marginal teeth ser- 

 rated, longer than wide. 



Genitalia: The genitalia of Ancylus is peculiar; the ovo- 

 testis is globular and the albuminiparous gland is very large, 



FIG. 103. 

 Animal of ANCYLUS. (After Binney.) 



tubular, and placed very near the ovotestis; the oviduct and 

 vas deferens are long and the penis is very long. The figure, 

 from Bronn, is sufficiently characteristic without further de- 

 scription (Fig. 104). 



Distribution: North and South America, Europe and Aus- 

 tralia. 



KEY TO SPECIES OF ANCYLUS. 



A. Apex placed centrally, shell conic tardus 



B. Apex placed posteriorly and directed to one side. 



a. Apex placed near the posterior end and a little to one 



side of the center. Shell depressed-conic rivularis 



b. Apex placed near the posterior end, at or close to the 



margin of one side. Shell very oblique shimekii 



FIG. 104. 



Genitalia of ANCYLUS FLUVIATILIS. (Bronn, Klassen und Ordnungen 

 der Weichthiere, Malacozoa, taf. CIII, Fig. 16.) gh, ovotestis; gal, albu- 

 miniparous gland; nb, radula sac; p, penis; rs, receptaculum seminis; 

 s, salivary glands. 



122. ANCYLUS RIVULARIS Say, pi. xxx, fig. 29. 



Ancylus rivularis SAY, Journ. Phil. Acad., Vol. I, p. 125, 1819. 



