118 



CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



VENERICARDIA PI.ANICOSTA MERRIAMI, new subspecies. 

 Plate 11, figures la and lb. 



This subspecies of V. planicosta is apparently the end mem- 

 ber of an evolutionary series which begins with the typical V. 

 planicosta in the Martinez, the Lower Eocene group of Cali- 

 fornia. The middle member is V. planicosta hornii (Gabb) of 

 the lower Tejon. This form in the adult stage lacks the 

 marked radial ribbing of V. planicosta hornii (Gabb), and it is 

 in general a higher form as well. The concentric ribbing of 

 this form is much stronger than that of the lower Tejon sub- 

 species. Young individuals, however, resemble the lower 

 Tejon form so closely that one is not warranted in recognizing 

 the subspecies upon the basis of the immature forms. 



Dimensions : Height, 70mm ; length, 70mm. 



This subspecies resembles V. potapacoensis Clark & Martin, 

 of the Maryland Eocene in that the radial ribbing in both 

 forms is becoming obsolescent. They appear to differ in shape, 

 however. The type, which is figured, is an extreme case of lack 

 of radial ribbing. Other specimens associated with it at the 

 same locality show fairly distinct ribbing in the neighborhood 

 of the umbones. This species is one of the most characteristic 

 forms of the Siphonalia sutterensis Zone. It occurs abundantly 

 but poorly preserved at a University of California locality eight 

 miles south of lone, Amador County, California, at the O'Neill 

 Sandstone Quarry, Sec. 27, T. 5 N., R. 10 E., Mt. Diablo 

 B. L. and M., in strata which were previously recognized as 

 lone. It is associated at this place with Meretrix hornii Gabb, 

 Turritella merriami Dickerson, and a few other species. This 

 fauna proves the lone to be only a facies of the Tejon Eocene. 



Type:— No. 241, and cotype, No. 242, Cal. Acad. Sci. Lo- 

 cality 25, Roseburg Quadrangle, Oregon, near the center of 

 Sec. 19, T. 26 S., R. 3 W., on the east bank of Little River, at 

 its confluence with the Umpqua, underneath the bridge at that 

 point. 



Named in honor of Professor J. C. Merriam of the Uni- 

 versity of California. 



