126 University of California Publications in Geology [Vol. 11 



Y. cooperi tenuissinia resembles Y. oregoni Shumard redescribed 

 by Dall ; 97 it differs from that species in the following respects : The 

 beaks are more posterior ; the posterior-rostrate end is somewhat more 

 attenuate and there are fewer teeth on the posterior margin. On 

 Y. cooperi tenuissinia there are thirty-two to thirty-five teeth 

 anterior to the beaks and about twelve posterior. Dall states that on 

 I". oregoni the number is thirty-two and seventeen. In the descrip- 

 tion of Y. oregoni 99 Dall states that Y. cooperi Gabb has fourteen 

 teeth posterior and forty anterior. The type specimen of Y. cooperi, 

 which is in the collections of the University of California, has only 

 eleven teeth posterior and about thirty-six anterior. A Recent speci- 

 men from San Pedro, also in the University of California collections, 

 has the same number of teeth as the type. Two specimens of 

 Y. cooperi from the Pleistocene of San Pedro, examined by the writer, 

 show some variation in the number of teeth ; one has fourteen teeth 

 posterior and forty anterior, the number given by Dall as character- 

 istic of the species ; the other has eleven posterior and thirty-nine 

 anterior teeth. The writer does not have enough specimens of 

 Y . cooperi of the Recent and Pleistocene to say whether there is a 

 constant difference in the number of teeth between the Recent forms 

 and those of the Pleistocene. It is possible that the Pleistocene form 

 should be considered as a distinct variety. 



YOLDIA cf. OREGONA Shumard 



Several specimens of a species of Yoldia collected at University 

 of California localities 78 and 1131 appear to be very close if not 

 identical with what Dall has listed and figured as Yoldia oregona 

 Shumard,"'' and which came from beds referred by him to the Miocene 

 from the Willamette Valley south of Oregon City, Oregon, and which 

 beds are now believed to be of Oligocene age. 



9' U. S. Geol. Surv., Prof, paper no. 59, p. 105, pi. 19, fig. 4, 1909. 

 98 For original description of Yoldia cooperi, see Geol. Surv. Calif., Palaeon- 

 tology, vol. 2, p. 31, pi. 9, fig. 54, 1866. 



oo U. S. Geol. Surv., Prof, paper no. 59, p. 105, pi. 19, fig. 4, 1909. 



