210 PLANORBIS. 



24. p. CENTERVILLENSIS, Tryon. 



Plate 7, fig. 7, 8, 9. 



Shell small, of four rather elevated whorls, 

 well rounded, slightly angled on the peri- 

 phery, suture well impressed, umbilicus nar- 

 row and deep ; aperture slightly dilated, quite 

 oblique. 



Diam. 4, alt. 1*5 mill. 



Inhabits Centerville and other localities in 

 Qalifornia. This is the Californian represen- 

 tative of our PL dilatatus, from which it dif- 

 fers in its larger size and greater proportional 

 height. 



25. PLANORBIS ALBUS, Milll. 



Hald. Monog. p. 29, t. 4, fig. 8—10. 



Its southern distribution has been ascer- 

 tained to extend as far as the District of 



Columbia. 



(57) . 



