384 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



It was not until after 1883 that King's term PlatystropMa came into 

 general use.* 



Several recent investigators have added mucli to our knowledge by 

 their specific interpretations, among whom Prof. E. R. Cumings and 

 Dr. A. F. Foerste ^ are most prominent. Professor Cumings pub- 

 lished a detailed study on the Morphology of the Genus ^ which 

 brought out the fundamental lines of evolution and viiriation. The 

 aim of the present paper is to corroborate and add some facts to the 

 work which he has done. 



The mutability of species has been accepted by most investigators 

 since Darwin published his "Origin of Species" in 1859. However, 

 many systematists to-day find difficulty in including more than one 

 species in a well-graded series, even though the extremes are quite 

 different. When individuals possessing common characteristics and 

 possessing the tendency to acquire certain other characteristics are 

 subjected to varying influences they develop differentially. This 

 results in groups which differ to a greater or less degree. These 

 groups are regarded by the writer as species. 



The material on which this study is based belongs for the most 

 part to the United States National Museum. It consists of about 

 4,000 specimens from various points in North America and Europe. 

 The specimens were mainly from the Ulrich collection, with addi- 

 tions made in recent years by various members of the museum 

 paleontological staff. 



In addition to these, several hundred Piatystropliias from the 

 Paleontological Museum of Columl)ia Uni^'e^sity v/ere at the writer's 

 disposal. Dr. A. F. Foerste also kindly presented about 500 speci- 

 mens from the Ohio Valley and from Michigan to the United States 

 National Museum in order to further the present study. 



With the fullest appreciation of Professor Cumings's work on the 

 "Morphogensis of Platystrophia" the writer gladly acknowledges 

 her indebtedness to him for the inspiration received from that valuable 

 work. He has also been of great service in offering helpful suggestions 

 and criticisms. Acknowledgments are extended to Dr. E. O. Ulrich, 

 of the United States Geological Survey, who supplied information 

 which could not be secured from any other source. The writer 

 desires to express her appreciation to Dr. R. S. Bassler, curator of 



t Zittel, Handb. Pal., vol. 1, 1880, p. 675.— Hall, 36th Rep. N. Y. State Mus. Nat. Hist., 1883, p. 34; 

 Rep. N. Y. State Geol. for 1882, 1883, p. 34.— Waagen, Mem. Geol. Surv. India, Pal. Indica, ser. 13, vol. 

 1, 1884, p. 549.— Shaler, Mem. Plentucky Geol. Surv., vol. 1, pt. 3, 1887, pp. 43, 44.— Hall, Bull. Geol. 

 Soc. America, vol. 1, 1889, pp. 19, 20.— Hall and Clarke, Pal. New York, vol. 8, pt. 1, 1892, p. 200.— 

 Winchell and Schuchert, Geol. Minnesota, vol. 3, 1893, p. 454.— Hall and Clarke, Eleventh Ann. Rept. 

 New York State Geol., 1894, p. 268.— Koken, Die Lietfossihen, Leipzig, 1896, p. 235.— Schuchert, Bull, 

 U. S. Geol. Surv., 87, 1897, p. 308.— WysogorsW, Zeits. d. d. Geol. Gesell., vol. 52, 1900, p. 234.— Cumings 

 and Mauck, Amer. Journ. Sci., ser. 4, vol. 14, 1902, p. 9; Cumings, Amer. Journ. Sei., scr. 4, vol. 15, 1903, 

 p. 1.— Grabau and Shimer, N. A. Index Fossils, vol. 2, 1907, p. 257.— Cumings, Tliirty second Ann. Rep. 

 Dep. Geol. Nat. Res. Indiana, 1908, p. 891.— Schuchert, Zittel Eastman Toxtb. Pal., 1913, p. 381. 



1 Bull. Sci. Lab. Denison Univ., vol. 1, 1885, p. 80. 



' Amer. Journ. Sci., ser. 4, vol, 15, 1903, p. 1. 



