4 THE UNIVERSITY SCIENCE BULLETIN. 



The age of the beds is believed to be Miocene, a conclusion 

 reached from a study of the fossil mammals and plants, and 

 other geological features. A sufficient number of land and 

 fresh-w^ater shells has not been collected to have an important 

 bearing on the subject. However, the long geological life of 

 the molluscan genera found in these strata as compared with 

 the disappearance of families and perhaps orders of mammals 

 is a valuable commentary on the correlation of deposits else- 

 w^here by the two classes of fossils when they are found singly. 

 Not only have the mollusks passed through epochs of intense 

 climatic change but they have withstood one of the most violent 

 outflows of lava visible on the surface of the earth. Yet the 

 genera found in the John Day and Mascall beds are repre- 

 sented in and near the same region to-day with closely allied 

 species. 



Ammoyiitella lunata Conrad. 



Planorhis (Spirorbis?) lunatiis Conrad, Am. Journ. Conch., vol. VI; p. 315, pi. XIII, 

 fig. 8, 1870. Condon collection. Bridge Cr., Ore. 



Planorbis (Spirorbis?) lunatiis White, 3d. Ann. Rep. U. S. Geol. Surv., p. 448, pi. 

 XXXII, figs. 24, 25, 1880-'81. Published, 1883. 



Gonostoina yatesi Cooper. Stearns (in White), Bui. 18, U. S. Geol. Surv., p. 16, pi. 

 Ill, figs. 8-12, 1885. Cope and Condon Coll. 



Arnmonitella yatesi prcecursor Stearns, Proc. Wash. Acad. Sci., vol. II, p. 656, pi. 

 XXXV, figs. 8-12, 1900. Same figures reproduced as in Bui. 18, U. S. Geol. Surv., cited 

 above. 



Aminonitelltt yatesi prcecursor Stearns, Science, New Series, vol. XV, p. 153, 1902. 

 Universit.v of California Collection. 



Ammonitella yatesi prceeursor Stearns, Univ. of Calif. Pub. Geol., vol. V, No. 3, p. 67, 

 1906. 



Although Conrad's description is very meager, taking it to- 

 gether with his figures leaves no doubt that he first described 

 the shell which seems to have been collected by many exploring 

 parties into the John Day region. His specimens were col- 

 lected by Thomas Condon, the pioneer in the field and it is 

 stated that they came from "Bridge Creek, Oregon." The 

 error in considering it to be a species of the fresh-water genus 

 Planorhis is not strange since Cooper says of Ammonitella 

 yatesi {Am. Jou7\ Conch., IV, 210, 1868) : "It would have been 

 supposed to be a Planorhis if found near water, and if the 

 streams of that country (Calaveras county, California) had 

 not been thoroughly searched by many collectors." 



Stearns first identified the fossils as A. yatesi Cooper but 

 later reconsidered the matter and made them a new subspecies 

 based chiefly on size. He says : "Though the fossil specimens 

 are considerably larger than any of the recent ones, I am un- 



