152 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



No one would mistake the two, liowever, even at first sight, since the 

 apex of Fisherola is more posterior than in Ancylus, while in Lmix it 

 is very nearly central. 



Named after Dr. \Y. K. Fisher, whose frequent criticisms during 

 the preparation of this paper have been much appreciated. 



Fisherola lancides, n.sp. PI. VIII, Fig. 35. 



Shell small, fragile, ovate-elliptical, broader anteriorly, low-arched, 

 concentrically striate, apex not inclined, sub-terminally posterior ; 

 habitat sluggish streams. 



Type: max. diam. 6, min. diam. 3'8, alt. l'2mni. Cotype : max. 

 diam. 5*5, min. diam. 4, alt. l"2nim. 



Columbia System in Snake River Basin. 



Snake River, AYashington (H. Hemphill). 



Genus Zalophancylus, n.gen. 



Type, Zalophaneyhis Bforani, n.sp. 



Shell of large size averaging 9 mm. in diameter, rounded-ovate, 

 regularly elevated-conic, concentrically and apparently radially striate, 

 apex central, large, and prominent, not inclined ; habitat apparently 

 lacustrine. 



Zalophanci'ltjs Morani, n.sp. PI. VI, Fig. 15. 



Shell of moderate size, regularly rounded ovate, elevated conic, apex 

 central and distinctlj' prominent ; habitat apparently lacustrine. 



Max. diam. 9, min. diam. 7, alt. 3-5 mm. 



Pliocene : Idaho Lake beds, Oregou. 



Badland Hills, one mile east of Sand Hollow, Oregon (R. B. Moraii). 



Named after Mr. R. B. Moran, who collected the type-specimens. 



Family PL.INORBID^ (H. & A. Adams), 1855. 

 Shell of minute, small, or moderate size, physiforra or planorbiform, 

 sinistral or ultra-sinistral,' sub-carinate above and below in early stages, 



The terms ultra-dextral and ultra-sinistral have seen frequent use in the 

 Lymnoids for genera in whicli the shell is dextral and the animal sinistral, 

 or vice versa. The explanation of Simroth and others is probably the 

 correct one, however, only in the present and one or two analogous 

 cases. It would be very difficult in the Kincaidilla stage of Gundlachia, 

 for instance, to explain this phenomenon in such a manner without the 

 animal living up on top of its shell, a feature the writer has never observed. 

 In the primitive Planorbidae, while the animal is dextral the shell is 

 obviously sinistral. In the more specialized stages an ultra-sinistral shell 

 is developed, doubtless the nearest approach possible to a dextral shell to 

 conform to the dextral animal, but there is no evidence that the ancestral 

 type was ever dextral. The development of Pompholyx offers similar 

 difficulties. 



In the three patelliform groups of Ancylidae — Acroloxus, Khicaidilla, and 

 Ancylus, for instance — Acroloxus is sub-sinistral, Kincaidilla sub-dextral, 

 while Ancylus is not distinctly either, yet the animal is sinistral in all 

 cases. It seems, therefore, probable that in this family, groups in the 

 patelliform stages exhibit no constant relation between the position of the 

 apex and the abortion of the soft parts. 



The families of the Lymnoidefe have doubtless evolved independently 



