APPENDIX. 025 



Genus GANGA, Layard. 



Operculum with the apex superior, slightly inclined, con- 

 centrically striate ; nucleus sub-central, dextral. 

 Ex. G. dilatata, Reeve. 



Genus TANALTA, Gray. 



Operculum with the apex lateral, lamellated ; nucleus lateral, 

 dextral. 



Ex. T. aculeata, Chemnitz (loricata, Reeve). 



Genus PHILOPOTAMIS, Layard. 



Operculum with the apex superior, paucispiral; nucleus sub- 

 basal, dextral. 



Ex. P. sulcatus, Reeve. 



Mr. Benson, in the "Annals of Natural History," for June, 

 1856, has stated that the nucleus of the operculum in Paludomus 

 proper is sub-spiral, which distinguishes it from Vivipara. He 

 adds, moreover, that the Philopotamis of Layard has a sub- 

 spiral operculum, which seems rather to indicate its place to be 

 among the Melaniidce. Serenia of Benson will stand as a syno- 

 nym of Tanalia, and Heteropoma of Benson as a synonym of 

 Philopotamis. The terminations of the species of Paludomus 

 should be feminine. 



Genus RIVULINA, Lea. 

 (Fam. viviPAKiDJ3.) 



Operculum like that of Paludina. 



Shell ovate, conical, smooth ; upper whorls dotted or lined 

 with brown ; peritreme continuous, with a slight depression 

 behind the columella in place of an umbilicus. 



Ex. R. modicella, Lea. 



To this genus must also be referred the species Zeylanica, 

 which, as well as modicella, we had included in the genus 

 Paludomus. 



