FRESHWATER GASTROPODA FROM MADAGASCAR. 



387 



The radula (fig. 1) exhibits a formula as follows :— 



?50. ?20. 1. 20? 50? =141. 



The transition between the lateral and marginal teeth is, as usual in these 

 forms, difficult to determine, so that the relative numbers constituting each 

 series must be left subject to query. 



The distinctive feature of the radula is the series of long, acute, and almost 



Fiff. 3. 



Fig. 2 



Fig. 2. Jaw of Ifethvema oleata (Ancey). (Reichert, 2 oc. x S obj.) 



Fig. 3. Genitalia of Methvenia oleata (Aucey). p, penis; ep, epipliallus ; pr, penis 



retractor ; vd, vas deferens ; Jl, flagellum ; v, vagina ; spth, spermatheca ; 



M, sperm-oviduct; ag, albumen-gland. 



straight marginals, which much resemble those figured for Rliysota Fouilloyi 

 by Burne {v. antea). Such teeth are of course met with in other genera 

 (e. g. Ariophanta), but never to the author's knowledge in combination with 

 the precise median and laterals here figured. 



The genitalia (fig. 3) are characterized by the long narrow penis and 

 epiphallus, and also by the cylindrical flagellum borne on the very long and 

 winding vas deferens at a considerable distance from the epiphallus. In the 

 female organs the distinctive feature is the length of the vagina. 



LINN. JOURN. — ZOOLOGY, VOL. XXXII. 32 



