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 navr- 
row and deep; aperture slightly dilated, quite 
oblique. 
Diam. 4, alt. 1:5 mill. 
Inhabits Centerville and other localities in 
California. 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, Mill. 
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) 
