96 



University of California Publications. 



[Geology 



ZAPATO CHINO CREEK, FRESNO COUNTY, CALIFORNIA. 



Saxidomus aratus Gld. Soutella gibbsi Rem. 



Clypeaster (Scutella) brewerianus Nevcrita recluziana Petit. 



Rem. Nassa calif omiana Com-. 



Astrodapsis tumidus Rem. Peel en sp. 



TAR RANCH. 



Chione s\>. 



Scutella i/iblisi Rem. 



Nevcrita recluziana Petit. 

 Zirphaea dentata Gabb. 



Tapes staminea Conr. 

 Area trilineata appears first in the San Pablo, though how 

 far down in this formation is not yet certain, and extends 

 through tlie lower and middle Merced, disappearing somewhere 

 between the Middle Merced and the Upper Gastropod Bed of the 

 Seven Mile Beach section. It is most abundant in the Lower and 

 Middle Merced. 



Description. — Rhomboidal, inequilateral, nearly two-thirds 

 of the length being behind the beak, posterior margin making a 

 very obtuse angle with hinge-line. Ratio of length to height, 

 about 1% to 1. Average size of adult about 51x33 mm. Beaks 

 not prominent, turned rather sharply forward, narrow and close 

 together, ligament area narrow. Hinge line long and straight. 

 Basal margin nearly parallel to hinge line. Ribs 26-32, usually 

 27. prominent, square, flattened, a little wider than the inter- 

 spaces and marked with a median groove. Occasionally, in the 

 older specimens, two subsidiary grooves may appear toward the 

 margin, as in A trilineata. More or less distinct lines of growth 

 often roughen the shell, especially in the larger individuals, and 

 when these are fine and numerous they approach closely the 

 beaded effect of A. trilineata. 



This shell is distinguished from A. trilineata and A. canalis 

 by its more inequilateral form, low, narrow beak, greater pro- 

 portional length, long straight hinge-line and generally less in- 

 flated shell. The latter characteristic, together with the median 

 grooves on the ribs, distinguishes it from .1. microdonta. 



Occurrence and Associated Fauna. — This species occurs most 

 abundantly in the sandy phases of the Monterey Miocene asso- 



ARCA MONTEREYANA, 116W Species. 

 Plate 9, Figs. 5, oa and 5b. 



