CONTENTS OR VOL. XX. 



ARTICLE I. 



The History of the Pelycosauria, with a Description or the Genus Dimetrodon Oope. By G. Baur and 



E. C. Case. (With 8 plates) 5 



ARTICLE II. 

 The Chronological Distribution of the Elasmobranchs. By 0. P. May 68 



* ARTICLE III. 



Results of observation with the Zenith Telescope of the Bayre Observatory from January 19, 1894, to August 



19, 1895. By Charles L. Doollttle 7,; 



ARTICLE IV. 



A Study of the Chromosomes ol the Germ Cells of Metazoa. By Thomas il. Montgomery, Jr., Ph.D. 



(With 5 plates) 154 



ARTICLE V. 

 Fossil Mammalia, of the White River Beds of Montana. By Karl Douglass. (With 1 plate) . . . 237 



ARTICLE VI. 



Results ol' Observation with the Zenith Telescope of the Bayre Observatory from April 1. 1878, to December 



37, 189;!. By Charles L. Doolittle 280 



