Vol. IV] DICKERSON—SIPHONALIA ZONE, OREGON -^2^ 



persistent ribbon-like band, much wider than the space between 

 these spiral lines, about half-way between the tuberculated 

 shoulder and the median groove. This line occurs on most 

 specimens. 



Dimensions : Length, 34mm ; width of body-whorl, 29mm. 



This species can be distinguished from Pseudoliva volutcu- 

 formis Gabb by its greater number of nodes, by the double an- 

 gulation of the body-whorl, and by the greater strength and 

 abundance of its spiral lines. The spiral lines of this species 

 resemble those of P. lineata Gabb, but they are stronger and 

 larger ; the tuberculations, however, make it easily distinguish- 

 able. This form appears to have been evolved from P. lineata. 



Type : — No. 248, and cotype. No. 249, Cal. Acad. Sci. Lo- 

 cality 25, Roseburg Quadrangle, Oregon, on Little River at its 

 confluence with the Umpqua, underneath the bridge at that 

 point. Coll., Bruce Martin. 



Named in honor of Professor J. S. Diller of the U. S. Geo- 

 logical Survey, whose mapping of the Roseburg Quadrangle 

 made the zonal connection between the Eocene of Oregon and 

 California possible. 



