Vol. VII] DICKERSON— CLIMATE AND OLIGOCENE FAUNAS 181 



of very fine radial lines roughly alternating in size further 

 decorate the shell. 



This form is much more depressed than H. ornata, new 

 species from same locality and its decoration is very different. 



Dimensions:— Length, 13 mm.; height, 3.5 mm. 



Type:— No. 436, cotype 437, Cal. Acad. Sci. Locality 181, 

 near Vader, Lewis County, Washington, on east bank of the 

 Cowlitz River, just back of the Greeco ranch house, about four 

 miles east of Vader. Colls., F. M. Anderson and Bruce Martin. 



Named for Dr. Ralph Arnold, who first described and recog- 

 nized the Oligocene strata of Washington. 



Hipponyx ornata, new species 

 Plate 31, Figs. 12a and 12b 



Shell with high apex bent forward so that it distinctly over- 

 hangs anterior; anterior end is vertical; posterior slope meeting 

 base at an angle of about 30 degrees ; very numerous, sub-equal 

 rounded radial ribs which become nodose at junction with con- 

 centric growth lines forming principal decoration. 



Dimensions: — Length, 10.5 mm. ; height, 5 mm. 



Type:— No. 439, Cal. Acad. Sci. Locality 181, near Vader, 

 Lewis County, Washington, on east bank of the Cowlitz River, 

 just back of the Greeco ranch house, about four miles east of 

 Vader. Colls., F. M. Anderson and Bruce Martin. 



Acmaea simplex, new species 

 PI. 31, Figs. 11a and lib 



Shell, small, high, smooth except for concentric growth lines, 

 with apex at one-third of length from anterior end; anterior, 

 with very steep slope. This forni is very similar to, or identical 

 with, a small species found in some limestones at the head of 

 San Lorenzo River in Santa Cruz County. 



Dimensions: — Length, 6 mm. ; height, 3.5 mm. 



Type:— No. 438, Cal. Acad. Sci. Locality 181, near Vader, 

 Lewis County, Washington, just back of the Greeco ranch 

 house, about four miles east of Vader. Colls., F. M. Anderson 

 and Bruce Martin. 



