Ball.] 46 [December 6, 



kalia Stiedce and those above mentioned, there do not seem to be any 

 characters by which the group can be differentiated from Tryonia. 



SCHEDULE. 



Genus Tryonia Stimpson. 

 Type T. clathrata Stimpson, 1865. 

 Syn. Leucosia Dybowski, ez parte, non Fabr. 

 Ligea Dybowski, ex parte, non Fabr. nee. Duponc. 

 Limnorea Dybowski, non Peron and Lesueur, nee Lamoroux, 

 Leach, Dana, et cet. 



Baicalia Martens, Apr. 1876. 

 Liobaicalia Martens, ex parte. 

 Trachybaicalia Martens, ex parte. 



SPECIES FROM LAKE BAIKAL. 



Tryonia Godlewskii ; T. Florii ; T. oviformis ; T. carinocostata ; 

 T. turriformis ; T. costata ; T. Wrzesniowskii ( !) ; and T. contabulata 

 Dybowski, sp. ; T. angarensis Gerstfeldt, sp. 



? Subgenus Baikalia Martens, emend. 

 Type B. carinata Dybowski, sp., op. cit. pi. iv. f. 1 -4. 

 ? Margin of the aperture notched anteriorly in the adult. 



Subgenus, Liobaikalia Martens, emend. 

 Type Liobaikalia Stiedce Dyb., sp., op. cit. pi. in, f. 20 -23. 

 Whorls loosely coiled, bearing a relationship to Tryonia analogous to 

 that borne by Lyogyrus to Valvata, and Camptoceras to Limncea. 



? Subgenus Dybowskia Dall. 



Type Ligea ciliata Dybowski, op. cit., pi.' in, f. 27-29. 



Whorls transversely ribbed, with a ciliate epidermis, deep suture, 

 short and rapidly tapering spire, and subcircular aperture. 



If specifically distinct from the type, which seems doubtful, Ligea 

 Duthiersii Dyb. also belongs to this section. 



The first species of Trachybaikalia having been retained for the 

 genus with which it was synonymous, while the name Liobaikalia 

 would have been entirely inadvisable for this group even had it 

 originally been included in that section, it appears that a new name 

 is called for. 



The remarkable character of the fauna of this lake basin will be 

 found closely paralleled in the old Pliocene lake marls of both Europe 

 and America. The creation of such a large number of generic 



